Current DD Accumulations

Chemical Thinning

The 2001 chemical thinning season continues to be a challenging one. In general, we have experienced marginal weather conditions during the traditional thinning time. The weather forecast predicts a cold front moving through the area today (Tuesday) and cool weather persisting through Friday. Fruit size in most areas are near 15 mm or larger, thus fruit are approaching the stage of development where it will be difficult to thin. If thinners have not been used they should be applied by the end of the week, when warmer temperatures are anticipated. More aggressive thinning strategies will probably be necessary to achieve appropriate thinning. Caution is suggested in using high rates of NAA since high rates at this stage of fruit development may result in reduced fruit size. Aggressive strategies suggested at this time include thinner combinations using carbaryl at 0.5 pounds actual per 100 gal., 1 quart of oil per 100 gal., and NAA at 6 ppm. We believe that carbaryl or NAA used by themselves at this stage of fruit development and under the predicted weather conditions will result in little or no thinning.

Stripping and Pinching

Now is the time to practice ‘stripping' and ‘pinching' young central-leader type apple trees. Stripping (Fig. 1) is the process of removal competing (to the central-leader) young shoots in first and second leaf trees. Stripping is easiest and most effective when shoots are two to four inches long. These young shoots are ‘stripped' off the central leader for a length of about twelve inches directly below the rapidly growing leader's terminal shoot. Shoots can be either torn off (as cleanly as possible) or the tips of hand pruners can be used, whichever you prefer. Usually three to four or five of these rapidly growing, vertically oriented shoots are removed to ‘protect' the central leader. Stripping will also result in more desirable (closer to 90 degrees) crotch angles in young branches on the leader.

Pinching (Fig. 2) is a technique most commonly used on vertical-axis trained trees. It differs from stripping in that just the growing tip(s) of competing shoots is removed in the top third or so of last year's leader growth, being careful not to ‘pinch' the leader! Pinching is done (using fingers or pruners) in late May or early June when shoots are about six inches long, and can be repeated several times when a few inches of re-growth has occurred. Pinching serves a couple purposes in the top one-third of vertical-axis trees: it slows down vigorous, competitive growth to the leader; and it promotes flowering on one-year-old wood, thereby devigorating the top of the tree, which is a desirable characteristic of vertical-axis trained apple trees. Note that stripping or pinching should be avoided in blocks where fireblight has been a problem.

A Reminder From FSA

If you have crop insurance, don't forget to report (in writing) to your local Farm Services Agency (FSA) office suspected crop damage (i.e. frost/freeze, hail) as soon as you make a preliminary assessment of the potential loss. (FSA's regulations give you 15 working days to report the loss.) FSA needs this information to establish a claim for you should it become necessary when the damage positively results in a significant, non-harvestable crop loss. Also, growers of NAP (Non-insured Assistance Program) crops should note that the requirement that 35% of the crop in the county be affected has been removed. Now crop losses for peaches, plums, blueberries, etc. can be treated on an individual farm-by-farm basis. For more information, don't hesitate to contact your county FSA office.

Plum Curculio

Under the rainy and cool conditions of the past week, not a lot of people were motivated to drive from inland areas to ocean beaches. Instead, a lot of folks probably stayed pretty close to home and indulged in munching on goodies. Plum curculios behaved quite like humans this past week.

As indicated by traps designed to capture immigrating PCs at the Horticultural Research Center, few PCs moved from overwintering sites in woods toward orchards.

If PC captures in 2000 can be a guide, we can expect 2 or 3 more pulses of PC immigration before the last stragglers have reached their destiny: orchard trees.

In contrast to rather little movement of PCs into orchards during the past week, those that survived petal fall treatments of pesticide began to pick up the pace in terms of munching goodies. PC egglaying is favored by wet weather, especially when evening temperatures are sufficiently warm. Even though temperature in some areas was marginal, egglaying picked up considerably. The data below show amount of PC egglaying on the same perimeter rows of apple trees in the same 12 commercial orchards sampled in 2000 and 2001. Average date of end of petal fall across all orchards each year was May 14.

The data reveal that we are experiencing more PC injury this year than last year at the same point in time. If last year can be a guide, then we should be especially mindful of possible late-season immigration and subsequent injury, which last year picked up big time during the last 2 weeks of June.

This year, for the first time, we are also sampling for PC injury on interior rows of apple trees in the 12 commercial orchards. Data to date are as follows:

These data show that PC injury is thus far 10 times greater on perimeter trees than on trees in rows 3 and 5.

All of the above suggests that it may be wise to apply a spray against PC as soon as the weather permits. The spray will protect against another flush of immigrants when the sun returns, and it will take care of PCs already on hand. From here on, sprays applied only to perimeter trees should do the job of preventing further injury to fruit on perimeter trees as well as preventing movement to interior trees.

Leafminers

Some young sap-feeding miners have been observed in a few commercial orchards. Even in those orchards where mines are most abundant, mines have reached one per fruit cluster on only a handful of trees. As indicated in our recent messages, we expect first-generation miner development to be strung out over a long time period this year. We believe it's best to wait until the full expression of miner density is evident--probably some time in mid or late June--before making a decision as to whether it is necessary to treat against the second-generation.

Mites

The cool wet weather has not been conducive to buildup of either red mites or two-spotted mites. In fact, heavy rains knock mites off of tree leaves. At this point, few growers should be overly concerned with mites.

Bark Borers

As discussed by Dave Kain and Dick Straub in the May 21 issue of "Scaffolds" out of New York, this is the time of year to think about preventing injury by bark borers to fruit trees. In New York (and possibly also Massachusetts), 2 kinds of bark borers are prominent in apple trees: dogwood borers and plum borers. Both have expanded their host range to include apple trees, especially younger trees. Larvae gain entry through burrknots that form on above-ground parts of dwarfing rootstocks. Feeding of larvae within burrknot tissue is not all that harmful. But larvae can move from there to feed on inner bark (cambium) and eventually girdle the tree. Plum borers seem particularly prone to do this and are the greater threat to tree survival. In Western New York, blocks of apple trees near cherry, plum or peach trees are the most prone to attack by plum borers.

In trees with burrknots, look for reddish-brown frass as a sign of borer presence. Dig into the burrknot and look for larvae. Dogwood borer larvae are creamy white, whereas plum borer larvae are blackish-green or blackish-purple.

If larvae are found, it is advisable to spray apple tree trunks with Lorsban. Now is an ideal time to treat against both species. The longer one waits, the better foothold plum borers may get. The spray will protect tree trunks against invasion by newly hatched larvae, which arise from eggs laid by adults active from now into summer. Be careful to confine Lorsban spray only to tree trunks, as it is illegal to apply it to any part of the tree canopy.

If you find evidence of bark borers infesting even just a few apple trees in a block, it will pay to protect the rest of the block from infestation by applying Lorsban to tree trunks in the very near future.

Scab: Be Careful What You Wish for . . .

When I started saying we could use some rain, I wasn't asking for it all at once. The question is, what is going on with the scab spores. And the answer is that while we got rid of a large percentage of them, there are still enough left around to be of some concern.

That's not so bad, considering that the rain made fungicide applications difficult. The key concerns most people have probably revolve around whether they had adequate fungicide protection throughout these prolonged infections of the last week. There isn't an easy and sure answer. The amount of rain, in some areas exceeding 3 inches, could remove fungicide, and new tissue expansion could also dilute protection.

My advice is to be cautious. If you have any doubt about protection during the rain, apply one of the post-infection options. An SI (Nova, Rubigan, Procure) plus a protectant, or alternatively one of the strobilurines (Flint or Sovran) give excellent post-infection activity, up to 96 hrs. Remember that an SI application must be followed by a second application 7 to 10 days later to have full effect.

Given that we will probably have infective spores for a few more days, perhaps to this time next week, then two fungicide applications with an SI are not a bad overall plan. Alternatively, if protection was good going into this last week, then one more protective application may be enough for primary scab season, as long as one uses the maximum label rates of the protectant.