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The apple industry is the focus of updated restrictions on use of some formulations of chlorpyrifos, most notably Lorsban 50W. Last week, the EPA announced that they had reached an agreement with Dow AgroSciences in accordance with federal governmental emphasis on reducing potential exposure of children to pesticides. Despite “minimal impact on most agricultural uses”, the agreement stipulates that use of Lorsban 50W and 4E will be restricted to prebloom use only, effective December 31, 2000. To the best of our knowledge, the current Lorsban labels will stay in effect for the duration of the 2000 growing season; use during 2001 will fall under the new restrictions, along with modified residue tolerances and REIs.
In last week’s issue of Healthy Fruit, we theorized that the last plum curculios of the season had immigrated into orchards during the hot stretch of 6/2-6/3. Over this past weekend (6/10-6/11), this theory was certainly tested, as we endured ideal conditions for further immigration of late-coming PCs. Despite the hot, extremely humid conditions, only a few PCs were captured—indicating that the last major influx of immigrating PCs has passed. This stands in some conflict with projections based on accumulation of degree days, which suggest that 1-2 weeks (depending on geography) of residual coverage are still necessary for PC control.
Although immigration ceased about 10 days ago, it is apparent in a few monitored orchards that the mild surge of immigrating PCs in early June encountered unprotected border trees, as fruit injury caused by PC egglaying has risen steadily over the past 2 weeks. Statewide, the cumulative PC damage levels are as follow:
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Sampling Period |
Cumulative PC Injury |
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5/29-5/31 |
0.8% |
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6/1-6/3 |
2.0% |
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6/5-6/7 |
2.5% |
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6/8-6/10 |
3.4% |
Expectedly, orchards in which the residual insecticide coverage dwindled in early June have been hit the hardest; in the most recent complete sampling round (6/8-6/10), orchard-specific damage levels in perimeter rows ranged from 0% to 17%.
So, despite our opinion that surges in PC immigration have ceased for the season, orchards may continue to accumulate damage form PC that arrived in early June. As temperatures and humidity increase again late this week (6/16-6/17), we encourage growers to take one more look for evidence of PC activity in traditionally high-pressure areas to assess the potential for intolerable buildup of PC injury.
Early-season trap captures of adult leafminers suggested that scattered blocks were again facing risk of developing the extremely high mine densities seen over the past several years. With these data, about 10% of surveyed growers treated blocks against first-generation mines—certainly far less than the proportion of growers using first-generation treatments in 1999. Samples over the past week indicate that the first-generation mine load has not developed to particularly alarming levels, and we expect that few growers will need to opt for second-generation LM treatments.
In most sampled orchards, the low mine densities are fortunate, as the weather patterns of this spring stimulated a vast disparity in periods of egglaying (and subsequent mine development). What this indicates is that second-generation mines will be highly strung-out in development, and will not have uniform susceptibility to any single treatment. Because Provado is by far most effective against developing eggs and early-instar larvae, growers who do feel the need to treat against second-generation LM may need to consider the possibility of two treatments to compensate for the disparity in mine development.
It has certainly been a bad season to be a mite. European red mite populations started the season with low numbers of overwintered eggs, experienced poor egg hatch, developed slowly, and have had to endure the cool weather and periodic driving rains of the past several weeks. All of this has come together to keep ERM levels well in check, and few growers are facing a developing need for chemical control. However, ERM populations have shown a tendency to rebound quickly; as the season warms up and dries out, growers are advised to monitor ERM development in order to avoid uncomfortable late-season ERM infestation.
Clothespins are one of the most valuable young apple tree training tools. They are useful in the orchard's first and second leaf for positioning developing scaffold branches so that the angle of the branch in relation to the central leader (trunk) is as close to 90 degrees as possible. In fact, this is probably the single most important (and simplest!) tree training technique you can use in the life of your orchard! Clothespins should be removed later in the growing season once the branch angle has been established -- it only takes a few weeks for young, succulent apple shoot tissue to retain it's position. But don't just throw those clothespins back in the bucket! Reuse them on young shoots that perhaps need a little help in maintaining as close to a horizontal positions as possible. (A good rule of thumb is that no scaffold or secondary branch originating from the leader should assume an angle greater than 45 degrees from horizontal.) Simply hang one or two (or three!) near the end of young rapidly growing shoots and they will help bring the young branch into a more horizontal position over time. It might be assumed they also simulate fruit on the young tree and perhaps control vigor and bring the tree into earlier bearing. Of course the clothespins should be removed once the branch diameter becomes constricted by the clothespin jaws. For pictures of the technique, see:
www.umass.edu/fruitadvisor/Team_members/clements/
Now is the time to make sure you have effective weed control in orchard tree rows, particularly in intensive orchards using dwarf and semi-dwarf trees. Cornell University research has emphasized the importance of having good weed control this time of the year when trees are actively growing and setting fruit. Extensive weed competition now may result in reduced fruit set and less-than-ideal shoot growth. Again, this effect is more pronounced with dwarf rootstocks. The research has also suggested that two -- or at the most, three -- applications of glyphosate (Roundup, Monsanto Company) gives sufficient season-long control of annual and perennial weeds in tree rows. The first application should have been applied already (around bloom), with successive applications during the growing season as necessary. In fact, a little weed growth just before and during harvest is OK because it soaks up excess nitorgen, and provides some protection from soil freezing during the winter when it dies-back. Glyphosate is environmentally and applicator 'friendly' compared to some other herbicides which pose a greater risk to groundwater contamination and carry the 'Warning' or 'Danger' signal words. When used sensibly during the growing season -- i.e., do not use on 1st leaf trees, avoid spraying on windy days and contacting foliage, etc. -- glyphosate poses little risk to tree injury too.
While we have made it through the primary scab season, secondary infections have started to menace a few orchards, are are running crazy in unsprayed trees. With all of the wet weather, even small amounts of scab from early May have had lots of opportunities to spread. In fact, there may be 3rd generation infections in some trees.
This week is particularly critical. Check trees for scab. If you know you have scab, see if it is in check or spreading. If you find new scab or see that old infections are spreading, treat it now.
If we return to hot weather, full rates of captan will be good for relatively light infections. It can reduce spore production and protects tissue. For heavier infections, consider Flint or Sovran. Two applications of either fungicide about a week apart will reduce spore production, and so will slow or stop the spread of scab. Benlate or Topsin M plus captan can also be effective as a scab eradicant where Benlate or Topsin haven't been used a great deal.
The strobilurines (Flint or Sovran) or the benzimidazoles (Benlate or Topsin M) plus captan are also excellent early summer treatments for flyspeck and sooty blotch. It certainly has been wet enough to encourage these diseases, but early indications are that the inoculum load available for this season may be relatively low. It may be premature to use these relatively expensive or predator mite-toxic materials unless you also have a scab problem.
Many apples grown in New England show some sign of calcium deficiency late in the growing season or during storage. It is important that growers treat for know or potential deficiencies, since significant losses of fruit may occur. A series of foliar sprays is the simplest approach to alleviating calcium deficiency. Calcium chloride is the cheapest source for sprays, but all soluble calcium sources give the same results. Applications (specific recommendations are listed below) should begin in June and be repeated a number of times throughout the rest of the season. As many as eight applications may be used, but most growers do not feel that it is financially justified to spray eight times from early June to harvest. So, we recommend calcium application whenever another spray is made. In some cases, leaf injury may be greater when calcium chloride is combined with captan or guthion, but in most cases where sprayers are calibrated properly, injury is not a problem. Do not, however, mix calcium chloride with solubor.
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CALCIUM RECOMMENDATIONS |
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Applications should begin three weeks after petal fall and continue at two-week intervals until harvest. |
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Calcium source |
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Actual calcium |
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Calcium Chloride (29% calcium) |
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Calcium nitrate (19% calcium) |
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Add 2/3 ounce vinegar per pound of calcium chloride. Use of a surfactant in calcium chloride sprays may reduce the potential for foliar injury. Leaf injury may be greater when captan or guthion is mixed with chloride. Do not mix calcium chloride with Solubor. |
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You might ask why lime does not provide adequate calcium, since it has calcium in it. Unfortunately, if lime is applied at a rate necessary to raise fruit calcium, soil pH will be too high for apple trees. Soil applications of between 10 and 15 pounds of gypsum per tree, on the other hand, may be used to increase fruit calcium levels. The effects of gypsum are slow, however, usually requiring as much as two the three years to increase calcium levels sufficiently to reduce or eliminate deficiency symptoms.
Healthy Fruit is written by Dan Cooley, Ron Prokopy, Jon Clements, Starker Wright, Arthur Tuttle, Wes Autio, Bill Coli, and Duane Greene except where other contributors are noted. 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.
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