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Massachusetts |
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Volume 13-- 2001 Berry Notes is written by Sonia Schloemann except where other contributors are noted. Publication is funded in part by the UMass Extension Agroecology Program and grower subscriptions. A text version can be e-mailed to you if you contact Sonia Schloemann. Please cite this source if reprinting information. |
Summer
Edition 2001 #4
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Region/Location |
Growing Degree Days |
Soil Temp |
Accum. Precip |
|
|
1 Month Gain |
Total |
(4" depth) |
||
|
Cape Cod: Barnstable |
59 |
332 |
70° F |
2.15" |
|
Eastern: Hanson |
57 |
363 |
65° F |
1.00" |
|
Waltham |
55 |
484 |
60° F |
0.39" |
|
Central: Boylston |
56 |
346 |
61° F |
2.02" |
|
Western: Amherst |
46 |
446 |
55° F |
4.12" |
|
Great Barrington |
44 |
365 |
51° F |
2.06" |
(Source: UMass Extension Landscape Message #13, June 1, 2001)
STATE WEATHER SUMMARY For the Week Ending Sunday, June 3, 2001
Prepared by AWIS, Inc.
|
AIR TEMPERATURE |
GROWING DEGREE DAYS CUM SINCE MAR 1 |
|||||||
|
BASE-50F |
BASE-60F |
|||||||
|
STATION |
LO |
HI |
AVG |
DFN |
TOT |
DFN |
TOT |
DFN |
|
Ashburnham |
39 |
70 |
54 |
-6 |
311 |
+120 |
74 |
+54 |
|
Boston |
43 |
72 |
59 |
-5 |
429 |
+92 |
127 |
+77 |
|
Greenfield |
34 |
73 |
55 |
-9 |
332 |
-8 |
81 |
+17 |
|
New_Bedford |
41 |
72 |
60 |
-4 |
369 |
+33 |
84 |
+36 |
|
Otis_AFB |
45 |
70 |
60 |
+0 |
321 |
+121 |
75 |
+58 |
|
Plymouth |
37 |
73 |
59 |
-3 |
334 |
+113 |
74 |
+51 |
|
Walpole |
40 |
75 |
58 |
-4 |
416 |
+148 |
121 |
+83 |
|
West_Medway |
38 |
75 |
58 |
-4 |
412 |
+144 |
117 |
+79 |
|
Westover |
34 |
70 |
58 |
-7 |
443 |
+11 |
127 |
+30 |
|
Worcester |
42 |
69 |
56 |
-5 |
363 |
+128 |
101 |
+73 |
|
Worthington |
32 |
70 |
52 |
-7 |
255 |
+55 |
59 |
+34 |
(Source: New England Ag. Statistics Service, New England Weekly Crop Weather Report, Volume 21, No. 5, June 4, 2001)
Disease Management Update in Strawberries – Sonia Schloemann, UMass Extension
Prolonged wet weather always raises concerns about disease problems. Gray mold caused by Bortyris cinerea is the disease most often discusses in this context. But, other diseases can also cause significant damage and yield losses. Among these are angular leaf spot caused by bacteria and the ‘water molds’, red stele and leather rot caused by fungi.
Angular Leaf Spot
Angular leaf spot is a bacterial disease caused by Xanthomonas fragariae. This bacterium infects only strawberries. It is sporadic in New England, but it can be important when it strikes. This disease causes leaf, petiole and calyx spots in New England, but has been reported occasionally to kill plants in California. It is favored by wet, cool (65˚ F in day, 35˚ F at night) weather.
Symptoms - Tiny water soaked spots appear on the lower surface of the leaves, which are angular in shape because they are bordered by veins. When the leaves are held up to the light, the spots are translucent. When viewed normally, they are dark green. Later, the spots will grow together to form larger, reddish-brown irregularly shaped spots, which may become surrounded by a yellow ring. These larger spots often follow veins. The leaf will have a ragged appearance. Spots can also appear on the petioles and on the calyx of the fruit, darkening them and making the fruit less attractive. In wet weather, a thick fluid can appear on the undersides of the infected leaves, which will dry to a shiny brown varnish-like film. This fluid and film is diagnostic for this disease.
Control - If this disease has been a problem, rotate away from strawberries for at least one year. Remove as much leaf debris from fields as possible at the time of renovation. Space plants widely in the row and plant narrow rows to maximize air circulation within the row. Avoid working in the fields when the plants are wet. Scouting should begin in fields that have a history of the disease as soon as buds extend from the crown, and should continue until bloom. If symptoms are seen, discontinue irrigation unless needed for frost protection or if weather is very dry. If irrigation is needed, time it so that plant dry off from morning dew for 1-2 hours before irrigation is turned on and/or so that plants dry for 1-2 hours before dew settles on to the plants in the evening. Some guides recommend the use of copper containing fungicides for control of angular leaf spot. However, the general opinion is that copper is not very effective and may cause phytotoxicity if used improperly. Cultural practices that minimize wetness and maximize drying are the best options for controlling this disease. Cultivar selection can also help. Cavendish, Annapolis, Allstar, Honeoye and Kent are very susceptible to angular leaf spot.
Leather Rot
Leather rot is caused by the fungus . It can infect the crowns, runners, and fruit of strawberry, and many other plants as well. This disease is more common in southern and midwestern states than in the Northeast. When it does affect this area, losses can be quite high. This disease is favored by wet weather, and temperatures of approximately 60o to 80o F. It can progress quickly when conditions are favorable, causing huge losses in just a few days.
Symptoms - On immature fruit, brown to dark brown spots that remain firm appear. The spots expand quickly until they cover the entire fruit. The fruit appears dark and leathery in texture, inside and out. Mature fruit may become soft and be dull pink to lilac, or may remain a normal color. When the fruit is split open, it usually has a sharp, pungent smell. The fruit tastes quite bitter. A white fuzzy growth may appear on the fruit if conditions are moist or if it is placed in a plastic bag with a moist paper towel for a few days.
Control - The fungus, Phytophthora cactorum, is in the soil, and can infect fruit after being splashed onto it by rain or by the fruit being in direct contact with the soil. A thick layer of straw mulch is important to keep the fruit off the ground and to prevent the soil from splashing onto the fruit. Mulching with straw rather than plastic prevents the berries from sitting in water. This disease is worse in wet situations, so plant in well-drained soil and avoid compacting the soil around the plants. Plant narrow rows and space plants widely within the row to keep the canopy dry. Plant in an area with good air circulation and control weeds to improve air circulation. Irrigate in the morning so that plants dry quickly.
There are systemic fungicides that will help manage infections by P. cactorum. Ridomil Gold 4EC (mefanoxam) and Aliette (fosetyl-Al) are registered for control of leather rot and can provide significant control especially when combined with the use of the cultural practices mentioned above.
Red Stele
This disease is caused by the soil-borne fungus Phytophthora fragariae. Many commercial strawberry cultivars are susceptible to the red stele fungus while many are resistant to one or more strains. This root rot disease has become a serious problem facing strawberry production in the northern United States. The disease is most destructive in heavy clay soils that are saturated with water during cool weather. Once it becomes established in the field, the red stele fungus can survive in soil up to 13 years, even if no strawberries are grown during that time.
Normally, the disease is prevalent only in the lower or poorly drained areas of the planting; however, it may become fairly well distributed over the entire field, especially during a cool, wet spring. The red stele fungus may become active at 40˚ F. However, the optimum temperature for growth and disease development is between 55-60˚ F. Under favorable conditions of high soil moisture and cool temperature, plants will show typical disease symptoms within 10 days after infection.
Symptoms - When plants start wilting and dying in the more poorly-drained portions of the strawberry field, the cause is very likely red stele disease. Infected plants are stunted, lose their shiny green luster, and produce few runners. Younger leaves often have a metallic bluish-green cast. Older leaves turn prematurely yellow or red. With the first hot, dry weather of early summer, diseased plants wilt rapidly and die. Diseased plants have very few new roots compared to healthy plants that have thick, bushy white roots with many secondary feeder roots. Infected strawberry roots usually appear gray, while the new roots of a healthy plant are yellowish-white.
The spores of P. fragariae, which reside in infected soils, are attracted to developing strawberry rootlets. After infection, the roots begin to rot from the root tip upwards toward the crown causing a characteristic reddening of the inner portion (stele) of the root; thus, the name "red stele". The best way to identify the disease is to carefully dig up a wilted plant and peel off the outside portion of several roots. If the stele is pink to brick red or brownish red, the plant has the red stele disease. The red color may show only near the dead tip of the root or it may extend the length of the root. The red stele is best seen in the spring up to the time of fruiting. No other disease of strawberry produces this symptom.
Control - Red stele development is favored by cool, wet soil. As a result, proper site selection and preparation are both important management tools for this disease. Soil drainage (both surface and internal) should be good because red stele requires free water (saturated soil) in order to develop. Avoid low-lying areas which tend to have poor water drainage. If the site selected does not have good soil drainage, the strawberry planting should be established on raised beds of 10 inches or more. The raised beds will allow excess soil water to drain away from the strawberry root system, creating an environment less favorable to the disease causing fungi. In addition, less soil compaction will occur near the root system. Be sure to clean cultivators or equipment used to build raised beds to insure that soil is not being carried from red stele infected fields.
If a high-risk site is being planted to strawberries, select varieties with resistance to the red-stele disease. These include: Allstar, Darrow, Delite, Earliglow, Guardian, Lateglow, Lester, Midway, Redchief, Redglow, Sparkle, Sunrise and Surecrop. (Note: The varieties classified as "resistant" are not resistant to all strains of P. fragariae. Therefore, it is possible that a new planting may again succumb to the disease if the site has poor drainage or if the site is improperly prepared.) Also, inspect transplants carefully before putting them in the soil to be sure they are not already infected with red stele.
There are systemic fungicides that will help manage infections by P. fragariae. Ridomil Gold 4EC (mefanoxam) and Aliette (fosetyl-Al) are registered for control of red stele. If red stele develops in an established planting, these fungicides should help control the disease especially if used in combination with good cultural practices. However, fungicides should not be used on a routine or preventative basis. Such use would be uneconomical and might result in the development of resistance by the fungus to these materials.
New Jersey is reporting the peak in trap catches of cranberry fruitworm. This suggests that our peak should occur in about 1 week. Insecticide sprays should be timed for one week after the peak in trap catches. Keep monitoring traps regularly (daily or every other day is best now) to identify the peak catch for your area.
Fruitworm Control in Blueberries
Rufus Isaacs and John Wise, Michigan State University
Adult cranberry fruitworms and cherry fruitworms have been trapped in Michigan blueberry fields in the past week. These were found at sites in Berrien County and in farms away from the lake that were developing earlier than most farms, but we can expect the next warm weather to bring fruitworm emergence to the rest of southern Michigan. If they have not yet been deployed, pheromone traps should be set in place now and weekly checking should be done to monitor the fruitworm development.
The first capture of male moths is an early warning of fruitworm activity, rather than a signal to get on the sprayer. Male moths typically emerge before females, and both are needed before egglaying can start. In blueberries, the adult moth typically lays eggs on the exposed calyx cup, and egglaying can only start after some petal-fall. It also takes a few days from egglaying until fruitworm eggs hatch, which is the optimal time for first application of insecticides registered for use during bloom.
Based on observations in recent years, it takes approximately ten days from the start of adult flight to the first egg-hatch activity. So, growers seeing their first moths this week should consider applying a bloom-time insecticide late next week if temperatures remain in the 60’s and 70’s and moth captures increase. Looking for eggs is the most accurate way to ensure sprays are timed correctly, because no degree-day model is yet available for fruitworms. Fruitworms typically place their eggs in the calyx cup, and so look for an oval, yellow egg (cranberry fruitworm) or a flat, round shiny egg (cherry fruitworm). These are more common on edges adjacent to woods, in sites where high moth captures have been found.
Insecticide options are limited during bloom because of bee toxicity of most insecticides. However, B.t. (Bacillus thuringensis) and Confirm (tebufenozide) are both registered for use during bloom for fruitworms. B.t.s and Confirm must be eaten to be effective, and have their greatest impact when temperatures exceed 70° F because the larvae are more active. B.t.s break down quickly under UV exposure, and so repeat applications are recommended every three to four days. Confirm is an insect growth regulator, which disrupts normal development, killing moth larvae. It has excellent longevity and rainfastness, providing a good fit for use during bloom in Michigan. Applications are made at 16oz/ac timed to coincide with egg-hatch, i.e. about ten days after the start of adult captures in the traps. Good coverage is essential for optimal performance of both of these products, and so a spreader-sticker is recommended to get the residues into all the places where fruitworms will feed and ingest the insecticide. Both B.t.s and Confirm are products that will provide control of other lepidopteran pests, such as the leafroller and looper larvae that have been seen in some blueberry farms recently.
Post-bloom, growers can continue use of B.t. or Confirm, or can switch to broad-spectrum insecticides. Of these products registered for use post-bloom, Guthion, Imidan, and Lannate are highly effective against fruitworms. Guthion (azinphos methyl) is an organophosphate with contact activity against a broad range of insects, and 10-14 days residual activity. Imidan (phosmet) is an organophosphate also with contact activity, with 10-12 days residual activity. Lannate (methomyl) is a carbamate insecticide with strong contact activity against fruitworms, but with relatively short residual activity. Asana (esfenvalerate) is also now registered for fruitworm control, but it has a 14 day pre-harvest interval (see other article) and relatively short residual activity. These products are also likely to effectively control other moth larvae, such as leafrollers that can be present in blueberries after bloom. (Source: Fruit Crop Advisory Team Alert, Vol. 16, No. 6, May 15, 2001)
Canopy modification tips
Tony Wolf, Virginia Poly Tech. Institute
Grape producers in Virginia frequently deal with situations where grapevine canopies are excessively dense. The resultant shade and increased humidity result in increased disease, and decreased fruit quality. Much can be done to avoid this situation, but the activity must start early in the season, before shade and its attendant problems develop. An entire chapter in the Mid-Atlantic Winegrape Grower's Guide (MAWGG) (www.ces.ncsu.edu/resources/winegrape/) is devoted to this topic, so the point of this newsletter article will be to highlight the major considerations for purposes of review.
Shoot thinning: For most varieties, our experience suggests that good canopy architecture is achieved with a shoot density of around five shoots per foot of canopy. One common exception to that rule of thumb is for Seyval, whose abundant fruitfulness dictates a shoot density of three to four shoots per foot of canopy to limit crops (often with additional cluster thinning) to five or six tons/acre with non-divided training systems. With appropriate pruning, the need for shoot thinning can be minimized; however, we still usually remove one or two shoots per foot of canopy in this process. When: Start when shoots are 6 to 12" long and when flower clusters are apparent, and after the threat of spring frost; complete 2 weeks before bloom (about the end of May in northern VA) if possible. Shoot vascular connections to older wood become lignified at or shortly before bloom, making their removal more difficult after bloom. What to remove: For cordon-trained, spur-pruned vines - remove the distal shoot(s) of multi-shooted spurs. In other words, try to retain shoots closer to the cordon to serve as spurs in the following year. Where the option exists, remove nonfruitful shoots in preference to fruitful shoots, unless crop reduction is part of your strategy. Retain nonfruitful shoots, however, that might be in a position to serve as a spur in the following year. An example would be a base shoot originating directly from the cordon. This strategy helps to keep the one-year-old, fruiting wood close to the cordon. The thinning can be done on a per vine basis, or per foot of canopy basis. I find it easier to simply focus on one foot of cordon at a time (5 shoots) and not worry about the number of shoots per vine. Divided canopy vines: For GDC and lyre, hold to same concept of about 5 shoots per foot of cordon. Thin the upper 180° of the GDC cordon in preference to those shoots that are already angled down. Young vines: Refer to training instructions in MAWGG. Remove shoots from trunks if 50% or more of cordon is developed. Unless the shoots break cleanly, use pruners to remove to avoid stripping bark of trunk.
Shoot positioning: We position shoots in an attempt to uniformly distribute the leaf area over the available trellis space and to promote the formation of our intended training system. Thus, vertically shoot-positioned (VSP) training is not VSP unless the shoots are vertically trained upright above the cordon (or cane). A combination of foliage catch wires and manual "tucking" are usually used to facilitate this operation. When: As shoot length warrants. On VSP systems, the first set of catch wires is typically at 10 to 18" above the cordon. When the majority of shoots are at or above this point, the first round of positioning is done. Wait too long and the cordon (or cane) may rotate and shoots will be pointing down, or to the side. Trying to turn such shoots back up to a vertical plane results in a vase-shaped canopy; undesirably wide through the fruit zone, and narrowing through the catch wires. Some use movable catch wires to help position shoots. The wires are "parked" beneath the cordon during the winter, and pairs (either side of trellis posts) are brought up to a fixed position above the cordon, bringing the shoots into a vertical plane in the process. Various shoot "taping" or tying systems are commercially available to assist with keeping the shoots between or otherwise attached to trellis wires. Divided canopy systems: GDC: it ain't GDC unless the shoots are positioned downward on both curtains. Start a week or two before bloom, raking the shoots out and down. Wait a week if significant shoot breakage occurs. Repeat the positioning about 2 weeks after the first round. If you wait too long after bloom, the tendrils will intertwine shoots, and significant shoot breakage will occur if you attempt to position the shoots. Timing is everything. For Scott-Henry, Smart-Dyson and Smart-Dyson ballerina, again, a two-stage process seems to facilitate the operation. The first stage, two weeks or so prior to bloom is aimed at getting the intended downward-oriented shoots out of their upward habit. Do not attempt to orient the shoots to the 180° degree position in one move; it's easier to move them to the 90° or 270° position now, and then come back at or just after bloom to further "encourage" them to the downward plane. Two grower tips: Lee Sandberg, Loudoun County, pointed out the need to time sprayer or other vineyard equipment traffic to avoid having to move in the vineyard when the shoots are hanging out - before shoots have been fully positioned into their downward plane. Dick Buttons et al. At Ivy Creek illustrated "fenders" that they mounted on tractors to deflect the shoots to avoid snagging or pinning by tires. Polyethylene water pipe work well for this (it bends before the tractor bends!).
Leaf pulling: Selective and judicious removal of leaves in the fruit zone aids fruit drying, reduces disease incidence, and may improve fruit composition through reduced acidity and improved color. Leaf pulling can also lead to sunburning and excessive acid reductions if overdone, so "selective" is an important qualification. When: First, don't pull leaves unless you feel your canopies will benefit from it. If leaf layer number is in excess of 2, and a majority of fruit clusters are hidden by foliage, there may be a compelling reason to pull some leaves. If so, try to accomplish the leaf pulling within the first 4 to 6 weeks after fruit set -- roughly the end of July with northern Virginia Chardonnay. Delaying leaf pulling into August increases the likelihood of causing sunburning as a result of the abrupt change in cluster light exposure. How many: What's your goal? If you're trying to reduce acidity in a variety like Norton, then maybe pulling all leaves in the fruit zone to maximize fruit exposure is desirable. Excessive exposure of some varieties, however, can lead to undesirably increased phenolic levels. Generally, pulling 2 or at most 3 leaves per shoot, from just around the fruit clusters is sufficient to obtain a desired response. If you find that you need to pull more than 3, chances are you have an excessive shoot density. I don't think that the goal should be to completely denude the fruiting zone. Our research vineyard at Winchester has north-south oriented rows. We typically only pull leaves from the east side of the canopy. This maintains some leaf cover on the west side and reduces the potential of sunburn from intense sun during the heat of the day.
Shoot hedging: Effective with shoot positioned canopies, hedging prevents elongating shoot tops from shading the fruit zone of VSP- or lyre-trained vines. There's not much point in hedging high-trained vines, unless you're concerned about the shoot tops being caught by machinery tires and ripped off. When: Before shoot tops begin to shade the subtending canopy. In wet years, such as 2000, you may need to top shoots 2 or 3 times. Alternatively, you might get away with a single topping in a dry year such as 1999. Heavy hedging after veraison can lead to lateral regrowth which may divert carbohydrates from fruit clusters until the lateral shoots become net exporters. How much: Key is how many leaves to retain. I advocate retaining about 15 leaves per shoot. This may be somewhat more than needed to ripen crop; however, it allows for a few to be pulled from around fruit clusters, Japanese beetle feeding, or other loss. (Source: May-June Viticulture Notes, May 24, 2001)
Phosphorus management in Michigan fruit crops
Eric Hanson, Michigan State University
Not all Michigan fruit crops respond to phosphorus (P) fertilization. As a general rule, tree crops and grapevines are the least likely to respond to P additions, and blueberries, strawberries and raspberries are the most responsive. Growers need to know how to recognize a P need and when applications are likely to pay. Unnecessary applications waste money and can increase the potential for pollution of surface water.
A typical agricultural soil might contain 1000 lb P/acre in the top six inches, but less than one percent of this may be in soil solution and available to plants at any time. The vast majority of P in soils is a component of organic matter and various minerals. These fractions serve as a slowly available P reservoir that replenishes solution levels. Plants absorb P from solution as either H2PO4- (dominant species when pH is less than 7.2) and HPO4-2 (dominant at pH greater than 7.2), although H2PO4- is preferred. The amount of P in solution is determined to a large extent by the nature and solubility of the P containing compounds in the soil. Soil solution P concentrations between 0.1 and 0.3 ppm P appear necessary for optimum production of crops, although this likely varies by species and stage of development. Fertilizer P added to soils undergoes various adsorption, absorption and precipitation reactions with soil components. The end result is that most fertilizer P adds to the soil reserves, and solution P levels are increased only slightly.
Soil pH has a considerable effect on P fixation and availability. Adsorption of P on iron and aluminum oxides limits solution P concentrations in acidic soils. Adsorption on calcium and magnesium minerals often reduces P availability in alkaline soils. As a result, P availability is generally optimized, and deficiencies are unlikely, if pH is near or slightly below 7.0.
Phosphorus fertilizers
Most P fertilizers are derived from phosphate rock (PR). Since PR is relatively insoluble, it is usually treated with either acid or heat to increase the solubility and availability of the phosphate to plants. The P content of fertilizers is expressed as percent P2O5. Ordinary superphosphate (OSP), triple superphosphate (TSP), are common phosphorus fertilizers derived from the acid treated PR. OSP contains 16-22 percent P2O5, of which 90 percent is water soluble, whereas TSP is higher is analysis (44-52% P2O5) and more soluble (95-98% water soluble). These P fertilizers are typically applied as blended fertilizers that also contain nitrogen and potassium.
For blueberries, mono-ammonium phosphate (MAP) and di-ammonium phosphate (DAP) are also good sources of both nitrogen and P. These fertilizers are very acidic, which often benefits acid-loving plants like blueberries. Plants also seem to absorb P more readily when it is applied in combination with nitrogen.
Determining P needs
The classic symptom of P shortage common to most fruit plants is uniform dark green to purple leaf color. With apples and pears, this color is most apparent in or near the main veins. Leaves are also smaller. In stone fruit crops, the dark green color may turn bronze or reddish purple. Petioles may turn red and older leaves may drop prematurely. Grapevines starved of P experimentally develop small dark green leaves, but deficiencies have not been observed in the field.
Although P deficiency is very rare in deciduous fruit trees, some orchards on very low P volcanic soils in the Pacific Northwest have exhibited deficiency symptoms, which included abnormally early fall color development on leaves. Strawberry and raspberry leaves turn dark green to purple, with the first symptoms developing on the older leaves. Deficient blueberry plants may be stunted, with dark green leaves and narrow, reddish twigs.
Tissue analysis is valuable in diagnosing P shortages. Tissue P levels considered deficient are less than 0.07 percent in blueberries, 0.2 percent in strawberries (newly expanded leaves) and raspberries, 0.1 percent in stone fruit, 0.12 percent in apples and pears, and 0.15 percent in grapes (petioles). If tissue samples are collected earlier than the recommended time in late July to early August, P levels may be higher than normal and these deficiency levels will not apply.
Soil tests provide a reasonable guide for P fertilizer needs for strawberries and raspberries, but not for blueberries, tree fruits or grapevines. Prior to planting any of these crops, soil P levels should be above 100 ppm. However, in established orchards, vineyards and blueberry plantings, soils levels below 100 ppm do not indicate a P deficiency. Soil test levels tell little about whether these plants will respond to added P.
Applying phosphorus
The most critical time to apply P is prior to planting. Phosphorus is nearly immobile in soils, so this is the only time to increase levels throughout the root zone of perennial crops. Thoroughly sample the soil before planting and incorporate P, as recommended based on the soil test results, along with needed lime and potassium. Preplant applications will usually provide adequate P for a several years (strawberries, raspberries) or even for the life of the planting in the case of orchards and vineyards.
In established fruit plantings, apply blended fertilizers containing P if tissue analysis or symptoms indicate a need. These materials should be applied when the nitrogen fertilizer is normally applied.
Why orchards and vineyards typically do not respond to P applications is not clear. Perhaps the roots of trees and grapevines mine enough soil to obtain sufficient P even when levels in the topsoil are marginal. These plants also form symbiotic associations with specific soil fungi (mycorrhizal fungi), and these relationships may also help the plants extract adequate P even from infertile soils. In some instances, P applications may be justified to maintain a healthy vigorous sod in fruit plantings.
(Source: Fruit Crop Advisory Team Alert, Vol. 16, No. 9, June 5, 2001)
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©Copyright 2001 University of Massachusetts Amherst, Massachusetts, 01003. (413) 545-0111. Produced and maintained by the UMass Fruit Team. This is an official page of the University of Massachusetts Amherst campus. |
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