Current DD Accumulations

Borer Blues

A reminder that borers (dogwood and plum) seem to be a growing problem in dwarf apples in the Northeast. Growers are advised to scout their young plantings of dwarf apple trees for the presence of borers NOW! A pocketknife can be used to dig-away the bark and frass to find the borer larvae buried just beneath the rootstock/burrknot surface. A severe borer infestation can result in girdling and death of young trees. The dwarfing rootstocks that form burrknots, such as M.9 and M.26, are most attractive to the borers, and those are just the trees to start looking at! Cultural practices such as clean herbicide strips, white trunk paint, removing plastic mouse guards, and deep planting or mounding of soil around the rootstock shank are helpful in keeping trees unattractive to borers. If, however, borer larvae are found in the rootstock, an immediate pesticide application is advised. Lorsban-4E has a supplemental label to use on borers, but only when applied to the trunk of apple trees (i.e., no foliar or fruit contact). This treatment is effective at killing borer larvae even though they are not exposed directly to the spray, and will also prevent adults from laying eggs. For more information on dogwood borers in dwarf apples, see the dogwood borer article on the UMass Fruit Advisor.

Calcium Clearly Calling

It is the time to start calcium sprays to improve fruit quality and storability. A season-long program of calcium sprays will help prevent fruit disorders such as cork spot, bitter pit, and senescent breakdown. Beginning three to four weeks after bloom, a total of eight foliar calcium sprays should be applied before harvest. Technical grade calcium chloride (CaCl2) should be applied at 2.0 to 2.7 pounds per 100 gallons dilute until mid-July, and then increased to 2.7 to 3.3 pounds thereafter. Foliar injury is possible with CaCl2 application, however, is minimized when using dilute sprays and sprayers are calibrated. Do not mix CaCl2 with Solubor, and when tank mixed with Captan or Guthion, leaf injury may be increased. For more information on calcium sprays, see the Fact Sheet ‘Foliar Calcium Sprays for Apples' on the UMass Fruit Advisor.

Hand Thinning

By now you should have a pretty good idea of fruit set of both apples and peaches. If you anticipate having to hand thin to reduce your crop load further, it's a good idea to get going on it as soon as possible. Early hand thinning is most effective at improving fruit size and promoting return cropping. Hand thinning is labor intensive, so make the most of it and get started early!

Note: Peaches are not immune to trunk borer problems. Look for borers right at the soil line, where their presence is indicated by a gummy, amber exude. Again, several borers per tree can result in yellow foliage and premature tree decline.

NAA to Increase Return Bloom

Naphthaleneacetic acid (NAA) can increase flower bud formation in apples. For a number of years some growers have added a little NAA to the spray tank at the end of June Drop with the hopes of increasing return bloom without thinning. Details and data in the literature to support this are vague. In general, NAA between 3 and 5 ppm is usually recommended, and it is applied one to several times in normal cover sprays.

Recently, Dick Unrath, Pomologist in North Carolina conducted a study using 5 ppm NAA in 3 different orchards.. He applied 5 ppm NAA starting 45 days after full bloom from one to four times at 2-week intervals. His results were that NAA significantly increased flowering for the following year in all cases. One application was as good as 4 in one block of Golden Delicious, whereas in a second Golden Delicious block at least two applications were necessary to increase flowering. On Delicious 4, applications increased flowering the most. In no case did these treatments hasten ripening or bring about additional thinning. The conclusion from this study was that NAA at 5 ppm can increase return bloom when applied at the end of June drop. The number of applications necessary to get the maximum response varied with the orchard.

Plum Curculio

Good news on the curculio front: the end may be in sight. Yesterday (June 11), we hit 343 degree days (base 50) since petal fall at the Hort. Research Center. According to the New York model, this means that little or no new PC injury should arise from now on provided insecticide coverage was good enough to handle PC through yesterday. Last year, the model predicted that the end of the PC injury season would be about mid-June. But we experienced our most extensive injury during the latter half of June, as shown below.

The model works well under dry or even average rainfall conditions but is subject to error under above-normal rainfall. This is because heavy rain can wash off pesticide and reduce residual activity below the 10-14 days built into the model. Last year we had a lot of heavy rain in June. This year, we had 2-3 inches on June 1-3 and another inch or so last night. Hopefully, we are now far enough along in the PC season that recent and future rainfall will not affect PC control.

As shown above, PC damage on apples in commercial orchards as well as on unmanaged trees nearly doubled this past week from what it was the previous week. As shown below, number of PCs captured on traps designed specifically to lure immigrating PCs also nearly doubled this past week compared to the previous week.

The very warm weather predicted for Wednesday through Friday should bring out the last overwintering PCs. Let's hope our insecticide coverage is good enough to handle these last immigrants and that we won't have a repeat of last year. If you traditionally are prone to high PC invasion and are in doubt, a border row spray may be good insurance.

Leafminers

Some leafminers have pupated, some are tissue-feeders and some are still sap-feeders, but by far the most never made it through the winter. Populations are very low almost everywhere in the state. Even though historically we can expect a 7-10 fold increase in miners from the first to the second generation, it seems as though few growers will be having much trouble with leafminers this year.

Mites

Like leafminers, mites also are a virtual no-show in most orchards thus far. The cool, rainy weather of the latter part of May and early June, coupled with effective oil applications, seems to have kept mites well in check.

One of the more important periods for making a mite-control decision is on the horizon. We can expect egg hatch of first-generation adults to begin in a few days. An assessment of population size of this new generation can best be made by examining mid-age (mid-size) interior fruit cluster leaves. If numbers of motile red mites exceed thresholds (roughly 50% of sampled leaves with one or more motiles), then it's the right time to apply Apollo or Savey (if that's what you were considering). These materials are maximally effective against eggs and young nymphs, which will be more synchronized in time within the next week or so that in any other time in the future. So if you were wondering whether or not to apply one of these materials, the time to sample and make your decision is coming soon. Horticultural oil, Vendex, Pyramite and Danitol are other miticides that can be effective.

Leafhoppers

This is the time of year when those of you who traditionally have had trouble with rose leafhoppers invading your orchard from nearby multiflora rose bushes may start seeing a lot of leafhopper adults flitting about your apple trees. This is a sign that trouble may be brewing, but it's too early to take action. Wait until these adults lay eggs and the nymphs hatch (late June or so) and then treat (if needed) with Thiodan, Provado or Sevin.

The first potato leafhoppers have been seen on apple trees, and we will discuss this pest more next week.

Green Leaf Weevils

In recent years, bright green weevils have become a more common sight on apple trees. These weevils confine their feeding to apple foliage and pose no threat to bearing trees. Like gypsy moths and tent caterpillars, however, they can cause a lot of harm to newly planted trees. Their consumption of growing tips can substantially stunt tree growth. Some growers who have experienced such damage have used Guthion or Imidan for control, but with moderate to little success. We have no alternatives to recommend, but Provado or Asara may be worth a try.