Apple maggot. Monday, August 21, 2017 Vol 24:20

Transcription

1 Monday, August 21, 2017 Vol 24:20 Apple maggot. Apple maggot (AM) traps captures within one week between checks were at or over the threshold level in about one third of the blocks checked last week (14 out of 45). Put another way, about a third of the blocks checked caught a treatment threshold number of AM flies within one week. (Note that some of these blocks had already exceeded threshold in prior weeks, and most had already received at least one insecticide application for apple maggot). Traps captures in two orchards with high Unsprayed Honeycrisp with extensive apple maggot infestation. AM populations (due to poor control last year in one case, and to a large reservoir of unsprayed apple trees nearby in the other) showed increased captures last week. Geneva and Hudson Valley New York research stations report peak AM trap captures on August 14 this year. Cumulative degree days in Sanford ME are about 8 days behind Geneva. If AM trap captures in Sanford peaked at the same cumulative degree day value as Geneva, then peak AM trap captures in Sanford would be August 22. Monmouth cumulative degree days are about two weeks behind Sanford, and 3 weeks behind Geneva. Based on this, AM trap captures in previous years, and the fact that dry soil conditions were relieved by soaking rain this weekend, it seems likely that AM emergence will increase this week. In the Sanford area, the August rain was over 2.2 inches. Regardless of which material was used for that application, it is reasonable to presume that there is no longer insecticide protection against newly emerged apple maggot where over two inches of rain fell. In other words, if the latest insecticide application was made before Saturday, August 19, the fruit are no longer protected against recently emerged egglaying AM. The situation is less black and white in Monmouth (Highmoor Farm) where there was less, but still substantial, 1.4 inches of rain on August The table below applies Monmouth rain observations to some simple rules for number of days and total rain since the most recent application to estimate the date after which fruit are no longer protected from apple maggot egglaying.

2 These day number and cumulative rain amount limits are not field validated, they are just my best guesses based on the residual efficacy table for AM insecticides shown in the July 25 newsletter. Of course, we do not know how much rain will occur over the next 10 days, and so the date estimates reflect the 10 deay rain forecast (which does not have much predictive skill beyond about 5 6 days.) Another best guess recommendation is to maintain protection at least through August 31 in order to be prevent damage from late emerging AM. Date of latest full dose application Estimated AM Protection End Date for Imidan (14 days, 2 rain) Rough Estimate AM Protection End Date for Assail, Endigo, Exirel, Leverage, Voliam Flexi (12 days, 1.5 rain) Rough Estimate AM Protection End Date for Altacor, Avaunt, Delegate, Entrust, pyrethroids (e.g. Danitol, Warrior etc.), Sevin (9 days, 1 rain) August 10, Thu. Aug 22 Aug 18 Aug 18 August 12, Sat. Aug 23 Aug 19 Aug 18 August 14, Mon. Aug 28 Aug 22 Aug 18 August 16, Wed. Aug 30 Aug 22 Aug 18 August 18, Fri. Sept. 1 Aug 22 Aug 18 August 20, Sun. Sept. 3 Aug 30 Aug 29 August 22, Tue. Sept. 5 Sept. 1 Aug 31 Each orchard is different, especially when it comes to AM damage potential. Having AM trap data was useful this year by providing information that because of a late start for AM activity, mid July, and in many cases, late July and even early August protection against AM was not needed in many blocks. If those same traps now show increased AM activity, that tells you that the protection not needed earlier is needed now. Knowing orchard history, and having AM traps in your orchard helps you determine if and when renewed insecticide coverage is needed. With harvest fast approaching, preharvest intervals become a pressing issue. For many locations, there is good reason to assume that renewed insecticide protection is needed after the heavy rain last weekend in order to protect against late season infestation by what could be a large portion of the annual AM emergence over the next few weeks.

3 White Apple Leafhopper, Woolly Apple Aphid. Keep an eye out for yellowish white White apple leafhopper (WAL) nymphs on the underside of leaves and treat if you find WAL on more than 50% of leaves. Assail, Avaunt, Endigo, Exirel, pyrethroid, Sevin or Voliam Flexi applied for apple maggot will also control WAL If white cottony Woolly Apple Aphid (WAA) are numerous on pruning wounds and leaf axils, control may be necessary to prevent staining of fruit and interference with harvest. Assail or one of the pyrethroid insecticides applied for apple maggot will also control WAA, as will Movento. See label instructions for adjuvant recommendations. Flyspeck and Sooty blotch. The 1 2+ inches of rain on August also removed fungicide coverage. As with apple maggot, growers need to evaluate whether the previous fungicide application was late enough, i.e. close enough to harvest, to prevent flyspeck colonies becoming visible before harvest. The amount of rain observed was less than the amount forecast, which shifted the dates for earliest safe final fungicide application to prevent flyspeck a bit earlier. Flyspeck colonies. application dates for fungicide protection to prevent visible flyspeck and sooty blotch before harvest. Dates assume protection against flyspeck development was adequate during June and July. Dates for Monmouth (and Sanford in parentheses), are based on observed weather, the 10 day forecast, and climatic averages beyond 10 days. Preharvest intervals are: captan and Pristine 0 days, Topsin 1 day, Flint 14 days, Sovran 30 days. For protection against visible Flyspeck through final harvest date of: application date for captan application date for Flint, Sovran, Topsin. application date for Pristine Sept. 20 July 29 (29) Jul 22 ( Jul 22) Jul 22 (Jul 22) Oct. 10 Aug 19 (19) Aug 11 (19) Aug 6 (19) Oct. 31 Aug 22 (26) Aug 19 (19) Aug 15 (19)

4 Roundheaded Apple Tree Borer. This is primarily for backyard orchardists. Roundheaded apple tree borer is rarely a problem in commercial orchards, presumably because insecticide applications for plum curculio and later apple maggot kill the female RATB before they can lay eggs. If you have failing trees with pencil diameter exit hole like this, that is a sign that RATB larvae have tunneled through the trunk for the past 2 3 summers and emerged this spring to mate and lay eggs to start a new generation. Where those insecticide applications are not made, the lower trunks of young tress less than 4 inches diameter should receive insecticide to prevent borer infestation, and the trees should be checked each May and August September to remove young borer larvae. The number of insecticide applications to the trunk needed depends on the material used. Chlorpyrifos (Lorsban) is the most effective material because it binds with bark and provides year long control. For other insecticides, the number of applications needed is not clear, at least to me. One recommendation apply lower trunk applications monthly in late June, mid July and mid August. Applying a latex paint whitewash not only helps prevent winter injury, but may also deter borer egglaying or reduce the number of hatched larvae that successfully penetrate the tree. An organic recommendation for which I also do not have efficacy data at this time is soaking the lower trunks in 1 or 2% neem oil formulation. The eggs are usually inserted into the bark near ground level during late June through August. The hatched larvae tunnel under the bark, producing sawdust like frass that is the best indicator of their presence (second photo). You can often find and remove the young larvae by digging them out with a sharp cutting tool. Some people claim success at tracking down larger larvae into their deeper tunnels into the wood. There is no point in looking for larvae in the large exit holes as those just show where an adult RATB exited the trunk.

5 Closing Words. Even After All this time The sun never says to the earth, You owe Me. Look What happens With a love like that, It lights the Whole Sky. ~ Daniel Landinsky Photo: NASA