Apple Pest Report: Friday July 18, 2008 Vol. 16 No. 8
Scab and Flyspeck
There isn‟t much scab around, but there is just enough in a few orchards to remind us that even after a dry spring, some early summer rains, and now an extended period without much rain, the apple scab fungus has not been eradicated from Maine. At this point, if you do find more than 5-18 scabby leaves per 100 shoots, a full dose captan application, followed by another in two weeks should keeps scab off of the fruit. As apple leaves mature, and as terminal shoot growth declines and the supply of succulent leaf area declines with it, the risk of apple scab infections proliferating decreases. In most cases, the amount of fungicide protection required to keep flyspeck and sooty blotch in check will be enough to a low level of scab infection from becoming an economic problem. If you haven‟t applied a full dose fungicide since July 1, then the flyspeck residual protection estimates on Orchard Radar indicate that fungicide renewal is needed because fruit are unprotected from earlier coverage. Sanford flyspeck estimates are at http://pronewengland.org/AllModels/MEmodel/RADARME-Sanford.htm#FLYSPECK and Monmouth estimates are at http://pronewengland.org/AllModels/MEmodel/RADARME-Monmouth.htm#FLYSPECK
Insects and Mites
As for apple maggot, this pest more than perhaps any other varies between farms, and even between blocks. That is why hanging apple maggot traps is so valuable. In the 23 orchards monitored by the Extension-Pom Soc scouting co-op, we have traps in one block at each orchard. At one location, we are counting over 20 apple maggot flies per trap per week. The
recommended spray threshold is cumulative catch of 1-2 AMF since previous insecticide coverage wore off. But that is the exception. There are one or two orchards with a few flies, which cumulatively over the past weeks have reached spray threshold. AMF trap captures in most blocks remain zero. As for mites, except for a couple of blocks at Highmoor Farm, all other monitored orchards have had very low counts. We‟ll keep looking however, and so should you. With hot weather mite counts can increase between weekly checks. This is particularly true of twospotted spider mites which can rear up as harvest approaches, and for which risk increases with dry weather making their alternate ground cover host plants less favorable.
Accurate dosage and good spray coverage are always important, none the less for those applications that are needed to protect the fruit as they approach harvest. This is a good time to reevaluate sprayer calibration. The two excerpts below may sound contradictory at first reading, but they refer to different situations. The first quote addresses situations where the calculated tree row volume (TRV) dilute gallonage for very small trees, combined with desired travel speed, and a sprayer designed for larger trees, results in a recommend gallons per minute output that is below the effective output range of the sprayer. If you are spraying very small trees with a sprayer designed for larger trees and higher water volume output, then rather than drive every row and have the pump operating at a gallons per minute output below its optimum range, it may be better to do an alternate row application and double the gallons per minute output. This approach relies on a powerful sprayer that can achieve good coverage across two rows of small canopy trees. It is worth noting that because the formula used for calculating TRV in the source publication is different than the formula used in New England, the problematic cases of getting good coverage on small trees would be estimated as ca. 125 gallon per acre trees in New England. My sense is that in Maine at least, getting good coverage on small trees is not a problem because most growers have mixed size plantings that include at least some trees of 10+ feet in height, and as a result sprayers are calibrated for the larger trees, with the only correction for very small trees being to shut off upper nozzles. As a general rule, this method of adjustment tends to result in applying more than the calculated amount of spray to the small trees. In other words, when the sprayer is set up to deliver a 4x spray to larger trees, using that same set up
and shutting off upper nozzles can result in smaller trees actually getting a 3x spray in terms of the volume of spray water. Because the tankmix dosage of pesticide was based on spray coverage being ¼ the dilute rate (i.e. 4X), then spraying the smaller trees at 1/3 the dilute rate (i.e. 3X) results in slightly more pesticide delivery to smaller trees than anticipated. Excerpt 1. “Dwarf high-density orchards represent a special situation for TRV applications. Most high density orchard TRV water application rates calculate out at well below the minimum desirable gallonage for good drop let impingement (below 150 gallons/acre). We have consistently found improved efficacy of pesticide application and improved time efficiency by calibrating for double the TRV. This raises the water application rate above the minimum desirable gallonage, and then you must drive every other row middle to reduce actual water volume per acre of orchard back to true TRV calculated rate. Pesticides are applied on a normal interval, alternating drive middles.” - 2008 Integrated Orchard Management Guide for Commercial Apples in the Southeast, senior editor, Jim Walgenbach, North Carolina State University. http://ipm.ncsu.edu/apple/orchardguide/orchard-management-guide.pdf The second excerpt below addresses situations where insecticidal control is less than satisfactory, and points to alternate row middle applications as one contributing cause. Inadequate coverage from alternate row application is much less likely to be a problem in the small trees referred to in the first excerpt, i.e. trees for which TRV dilute amount of water estimated by the TRV formula used in New England would be below 125 gallons per acre. “The foremost cause of control failure is the use of reduced rates, by design or by omission, through faulty sprayer calibration. Simply, most insecticides are rate responsive. The label will give a rate range and many lower rates will not provide acceptable control…. …A close second reason for control failure is poor coverage. The use of alternate row applications, high winds, or rains that wash off recently applied materials significantly reduce coverage and residue. Alternate row middle applications may provide acceptable control for highly mobile insects such as plum curculio or apple maggot but provide poor coverage for „non-mobile‟ insects such as the lepidopteran larvae. For OBLR, coverage is critical. Their leaf rolling and webbing habits allow for optimum exclusion from insecticide applications. No matter how big your sprayer is and how many rows you see the plume moving, you simply do not get the material into the canopy with alternate row middle applications. Couple alternate row applications with a low
range rate, less than optimum timing, then add 1” of rainfall, and the likelihood of control failure increases dramatically.” Scaffolds Fruit Journal, July 14, 2008. Peter Jentsch, Hudson Valley Laboratory, Cornell University. http://www.nysaes.cornell.edu/ent/scaffolds/2008/080714.html Dr. Andrew Landers, a nationally recognized expert on orchard sprayer technology will be conducting a full-day workshop with morning classroom session followed by afternoon outside demonstrations on April 14, 2009 at Highmoor Farm in Monmouth. Don‟t leave your taxes until the last minute next year so you can attend this great workshop with an undistracted mind!
“Agriculture not only gives riches to a nation, but the only riches she can call her own.” - Samuel Johnson