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Boron is essential for many plant processes. Deficiencies result directly in apple fruit disorders, but also reduce calcium uptake. Proper boron management is essential to your calcium-management program.
Boron can either be applied to the soil annually at a rate of 2-3 lbs of actual boron per acre. Alternatively, it can be applied foliarly at a rate of 3 lbs Solubor® (or other soluble boron source providing an equivalent amount of boron) per 100 gallons (dilute) in the first and third cover sprays (but no later than 30 days after petal fall). Concentrations should not exceed 6X, and take care to dissolve soluble pesticide bags in the tank before adding the soluble boron. Do not apply boron to peaches unless they are known to be deficient, and if they are, do not exceed 1 lb of actual boron per acre.
Magnesium is commonly deficient in Massachusetts apple orchards. Last season, if you noticed yellow or dead tissue between veins on the oldest leaves of new shoots, your trees may be deficient in magnesium. Often, some or many of these leaves drop from the tree prematurely, leaving “tufted” shoots, and ripening and drop are usually advanced.
To avoid deficiency, you should use dolomitic (high-mag) lime when liming or you should include magnesium sulfate in your soil applications (at the rate of about 100 lbs of MgSO4 per acre in early spring).
Foliar applications may be used to prevent deficiencies while soil problems are being corrected. Apply Epson salts (soluble magnesium sulfate) at the rate of 15 lbs per 100 gallons (dilute) at petal fall and in the first and second cover sprays. Avoid spraying during high-temperature or slow-drying periods. Epson salts is compatible with most pesticides, and should be applied at 8X or less.
Over the last ten years, we have discussed, on a number of occasions, ways of reducing apple tree growth and of encouraging flower bud formation. These techniques are particularly useful in settings where trees are planted too close or where trees are relatively young but appear uninterested in fruiting.
Girdling is one of the most reliable approaches. It can take the form of a single cut made with a knife completely encircling the trunk at the base of the tree (referred to as scoring) or a similar cut but with the removal of some bark tissue (referred to as ringing). Scoring is easily performed with a curved linoleum knife, and ringing can be done with a saw (for 1/16 inch cuts) or with a specially designed ringing tool (for 1/8 inch to 1/4 inch cuts). This is best done when terminal growth is between 4 and 6 inches, but it will be effective somewhat later. Generally, we recommend not girdling weak trees. It is best to use scoring primarily and ringing (with a saw) only sparingly.
For situations where the crop is lost due to frost or hail, ethephon can be an excellent treatment for reducing vegetative growth. Apply ethephon at 1.6 pints per 100 gallons dilute (500 ppm) when growth is 4-6 inches and again a month later if needed at 1 pint per 100 gallons (300 ppm). Do not use ethephon on fruiting trees, since it will cause some thinning and early fruit drop.
The bloom period was close to ideal in most areas of the state and bee activity was good. Bloom was heavy in most orchards. Trees have not been stressed this years so a heavy initial set of healthy developing fruit is expected. All of these factors suggest a more aggressive than normal thinning program should be adopted this year. Petal fall has occurred in most orchards in Massachusetts. Chemical thinning should be underway now.
Several thinning strategies can be used at petal fall. The most conservative and widely-used approach is to apply carbaryl at 0.5 lb ai/100 gal. Those that do not want to use carbaryl because of fear of harming mite predators may use NAA at concentrations ranging from 3 to 15 ppm. In this year of heavy and robust set, a combination spray containing carbaryl and NAA may be the most appropriate approach. Carbaryl at 0.5 lb/100 gal plus 6 ppm NAA is a middle-of-the-road suggestion for most varieties.
Ultimately, weather following thinner application will determine how successful thinning sprays will be. The weather forecast for the next 7 days is for favorable temperatures for adequate thinner response. This opportunity should be seized. Although the traditional time to apply chemical thinners is at the 8 to 10 mm stage of fruit development, unfavorable temperatures occurring at that time may preclude adequate thinning. This may be your best and perhaps your only time to thin.
There are local differences in response to chemical thinners. Check previous years chemical thinning records Erring on the more aggressive side this years seems warranted, given the crop potential and weather conditions.
As I write this, most apple growers should be sitting in their spray cabs. With the prediction of rain tonight and tomorrow, the last major infection of the season is bearing down for tonight through Thursday. This will probably be a serious infection period.
The primary inoculum levels are high. With several days of warm weather, a significant part of the season's ascospore inoculum has matured. The next daylight rain will release from 25 to 40% of the season's spores. If leaves stay wet long enough, and indications are that they will, then infection risk will be high.
At the same time, any infections that occurred during the week of May 3 will just be starting to produce conidia. These spores will also be available for infection.
The good news is that this wetting will be the end of primary scab season. With approximately 90% of the season's ascospores mature, there will be very little chance of primary infections after the next rains. Even later areas will be at the end of primary season by Monday (May 24). In these late areas, if rain stops by Friday, there is chance of a light infection period with wettings that come after May 24.
It is time to start checking for infections that might have gotten going a couple of weeks ago. These will be difficult to see for another week, so look carefully in areas that are most likely to develop scab - tops of big trees, corners, places where the wind always blows or you had to drive fast. Plan to check at least once a week for the next couple of weeks. If there isn't any scab in an orchard by June 7, chances are there won't be any this season.
Judging from captures across several hundred traps, plum curculio immigration through 5/16 was proceeding slowly. Since then, it seems that movement into and activity in orchards has heightened, and a scattering of PC egglaying wounds has been recorded in several monitored orchards.
As mentioned in last week's Healthy Fruit, PC flight into orchards occurs predominantly in the late afternoon through evening. Up to now, the weather has not been conducive to heavy immigration, as evenings have been too cool and dry. If the forecasted weather conditions hold (calling for increased evening temperatures and higher humidity), we expect that the rumblings of full immigration may come late this week (5/20-5/21).
Moister air, increased evening temperatures, and subsequent increases in PC immigration and activity may clarify the decision of timing the first treatment targeting PC. In most years, petal fall signals the start of PC management; with most orchards at or near petal fall, this is one of those years. Particularly in areas where king fruit have reached 1/4" or greater diameter, warm, humid weather can spark rapid accumulation of PC damage. Assuming that the weather continues to favor PC activity, growers are advised to keep a sharp eye out late this week for appearance of egglaying scars.
If treatment is deemed necessary, a border-row treatment with either Guthion or Imidan should be sufficient for control of immigration. However, if heavy egglaying is observed or if there is a need to control European apple sawfly or tarnished plant bug, a whole-orchard treatment may be in order.
As projected by record-high captures of leafminer adults on trunk traps, control of LM poses a substantial challenge in most commercial orchards statewide. In a recent informal survey of growers, the vast majority intends to use Provado to control first-generation miners. We know of no better approach to LM management, although Agri-Mek, SpinTor, and Lannate are also labeled as alternatives.
First-generation sap-feeding mines have begun to appear in many monitored orchards, and limited sampling has revealed 8-10 mines per cluster in some areas. In a few orchards with high early-season trap captures, mines are so numerous on older leaves that they are difficult to tell apart, as the limited available leaf surface cannot sustain the numbers of individual mines.
The appearance of sap-feeding mines is an indicator that the window for application of Provado, SpinTor, or Agri-Mek has opened; each of these materials is decreasingly effective as LM larvae mature. However, control of this pest has been made especially difficult by the weather pattern before and into bloom. LM egglaying was observed to occur in distinct waves into bloom, and it would be expected that sap-feeding larvae will appear in waves of similar frequency. This calls into question the residual activity of post-bloom treatments, as sap-feeding mines may appear over a period of two weeks or so.
According to the manufacturer of Provado, it is particularly active against leafminers and other sap-feeding insects because it is readily absorbed into the leaf tissue within a day of application. After absorption, it is estimated to retain its activity in the foliage for a period of about 7 days. If Provado is the material of choice, we recommend that an application be made as soon as sap-feeding mines exceed the following thresholds:
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We feel that a treatment of Provado triggered by the appearance of sap-feeding mines will offer good control of LM in most orchards. In areas with extremely heavy pressure, or areas where LM egglaying was spread out over a long period, some mines may survive treatment. In these areas, growers are advised to keep an eye out for the appearance and abundance of second-generation mines (generally in mid- to late June).
Young leafhopper nymphs have been observed in areas with perennial LH problems, but no feeding injury has been observed thus far. Given the need for fairly widespread use of Provado and Sevin this year, we do not expect that white apple leafhoppers will pose much of a threat in most orchards.
Even so, if only a petal fall application of Sevin was used, or if neither Provado nor Sevin was applied, growers should be conscious of immigrating rose leafhoppers and developing white apple leafhoppers. The third generation of this pest can cause substantial problems, from nuisance to pickers to deposition of excrement on fruit. Thresholds for treatment and management options will appear in next week's issue.
Pear fruit are approaching 1/2" diameter in some areas, and psylla hardshells have yet to appear. This bodes well for control of psylla from treatments made soon after petal fall, as post-bloom applications are very effective until hardshells begin to appear. Refer to last week's issue or the 1999 March Message for treatment recommendations.
Some areas under heavy early-season pressure from thrips are still experiencing problems, even though the trees are approaching petal fall. The continued thrips activity may be the result of secondary invasions, but it is more likely that some of the in-orchard population was able to survive treatment by very low rates of Imidan. In areas that targeted thrips with a quarter-rate of Imidan, some thrips are still active high in the tree canopies, while nearby orchards experienced excellent thrips control from a half-rate. Growers run a risk if thrips stay active through bloom, as their feeding within blossoms can reduce the quality of the flower parts and its attractiveness to pollinating insect. This may not be such a problem this season, as heavy bloom and high pollinating activity will likely offset the damage.
Healthy Fruit is written by Dan Cooley, Ron Prokopy, Starker Wright, Wes Autio, and Duane Greene except where other contributors are noted. Edited by Dan Cooley. Publication is funded in part by the UMass Extension Agroecology Program, grower subscriptions, and the University of Massachusetts IPM Program. A text version can be e-mailed to you if you contact Doreen York. Please cite this source if reprinting information.
