Apple Pest Report August 14, 2003

INSECT and MITE PESTS

Apple maggot Baited red ball traps at Highmoor Farm continue to catch apple maggot flies at a high rate.

The treatment threshold for odor-baited traps is an average of 5 AM per trap since protection from the previous insecticide has worn off. Usually it takes at least a few days to accumulate enough new captures to require a follow-up insecticide application. At Highmoor this year it did not take long after the previous spray was assumed to have been depleted before there were enough new captures indicating need to respray. As you can see in the chart , since July 23 AM have been caught at a rate of at least 3 per trap per day, and in some of the traps have caught 10 AM per trap per day.

The high trap captures are not limited to the 5 traps in blocks that received no insecticide last year and none this year until August 4. The 11 traps in managed blocks have also shown high captures.

Cornell researchers have found no need to apply insecticide on midseason cultivars like McIntosh and Cortland for protection against apple maggot after mid-August. However, that rule of thumb does not necessarily apply to later harvested cultivars.

Apple maggot populations vary tremendously between locations, so the Highmoor AM situation does not necessarily imply that AM are abundant state-wide. But if you do not have your own AM trap data, then it would be prudent to assume that this is not a year to take chances with apple maggot protection. If you do run your own traps, make sure they have enough stickum to be effective. Also, dead flies and other debris must be cleaned off occasionally as unattended traps lose about 25% of their capturing efficiency per week otherwise.

The recent rains depleted insecticide protection applied before August 10. Not renewing that protection could expose the crop to noticeable apple maggot infestation before harvest is complete. A final spray on August 10 may be inadequate this year given the abnormal amount of early August rain and potentially high apple maggot population.

Codling moth and other caterpillars

Second generation egg hatch is underway for codling moth, lesser appleworm, and redbanded leafroller.

Because we do not accumulate enough degree days, part of the second generation codling moth egg hatch either never happens or occurs too late for the larvae to complete enough development to overwinter. Codling moth overwinter as larvae inside protective cocoons underneath loose bark on trunks, on brush near trees, or even in corners of apple bins. But enough second generation larvae succeed to guarantee a codling population each spring. Also, some first generation larvae do not progress to second generation, but delay emergence until the following spring.

Codling moth and lesser appleworm primarily drill inside the apple from the calyx or stem end. A small pile of fine sawdust-like frass indicates their presence in an apple. Redbanded leafroller larvae feed on the surface of the fruit leaving an irregular shape gouge.

These species are not normally a problem where applications of Imidan, Guthion or Avaunt were made against plum curculio in June, and then against apple maggot in late July and August. If there are not many unsprayed apple trees near the orchard serving as a source immigrant codling moth females, then suppression of the first generation alone may prevent a threat from the second generation. But where there is a codling moth population, either from uncontrolled first generation that develop in the orchard, or from unsprayed apple trees within about 200 meters of the orchard, then second generation codling moth can cause more damage than the first generation.

Redbanded leafrollers feed on a wide range of plants. Therefore, there is high potential for second generation immigrants even if first generation control was excellent.

The concern about rain depletion of early August insecticide coverage mentioned above for apple maggot also applies for these potential pests. Most of the second generation egg hatch has yet to occur. If those young larvae are not killed by exposure to effective insecticide residue on the leaves and fruit, then there is potential for damage between now and harvest.

For organic growers, these are primary pests that need to be targeted by either Bt or Entrust applications. In organic blocks using Surround, repellence of first generation codling moth probably doesn't reduce the threat of second generation infestation. Surround is not recommended for use against second generation codling moth, which is a moot point since growers would not want to anyway because of wanting to prevent noticeable clay residue at harvest.

Bt or Entrust coverage over the next few weeks should pay for itself in reduced crop damage. It could take more than one application to maintain coverage long enough to prevent possibility of damage that becomes noticeable prior to harvest. The Codling moth respray guidelines online for Monmouth and the other 3 Orchard Radar sites are provided primarily to help with spray timing for Bt and Entrust.

With Imidan and Guthion, experience has shown that a mid-August final application has been late enough to prevent second generation codling moth, lesser appleworm and redbanded leafroller damage. Presumably, the same is true of Avaunt, and the 28 day preharvest interval limits how late you can spray Avaunt anyway.

Leafminers

Leafminer counts were far below threshold in 35 out of 40 blocks checked since August 1. Four of those blocks had borderline leafmine densities of just over 1 per leaf, one block had 1.7 per leaf. The Cornell threshold for second generation leafminer is an average of 2 sap-feeding mines per leaf. A lower threshold of 1 per leaf is prudent for McIntosh and other trees with increased chance of preharvest drop.

If leafminer control is needed, Avaunt offers control of both apple maggot and sap-feeding leafminers. Otherwise, separate applications would be needed for apple maggot and leafminer control.

Leafhoppers

Leafhoppers that you see on fruit cluster leaves now are probably rose leafhoppers. Potato leafhoppers feed on terminal shoot leaves and can stunt growth on young trees. Second generation white apple leafhoppers should start appearing around August 19 - 27 in the Sanford - Corinna areas.

Unless they exceed 3 per leaf, rose and white apple leafhoppers are unlikely to affect the crop, but their tar-like excrement spots and annoyance to pickers can require control at lower densities. Avaunt controls leafhoppers. But if you discover a leafhopper problem too close to harvest for Avaunt's 28 day preharvest interval, Sevin offers leafhopper control and a 3 day preharvest interval.

Mites

European red mite and twospotted spider mite counts continued to be low right through August 13. An increasing portion of European red mite eggs laid from this point on will be overwintering eggs that will not hatch until next spring.

Given the remarkably low mite populations in Maine this year, and really since 1998, I am contemplating IPM heresy and wondering whether blocks that had consistently low mite counts the previous summer really need prebloom oil next spring. Skipping the oil might increase the chance of problems with San Jose scale and aphids, but those are such rare problems that without need to control overwintered ERM, the difficulty and expense of an early season high water volume spray trip to apply oil may not be justified. However, skipping prebloom oil would require mite scouting at petal fall to see if an early season miticide (Apollo, Savey, Agri-Mek, or Vendex) is needed.

The recommended treatment threshold for mites until August 31 is finding an average of 7.5 living hatch mites per leaf, or finding one or more mites on 83% of middle-aged leaves. A mini-sample of 40 middle-aged leaves is below threshold if 18 or fewer of those leaves have mites. A 40-leaf sample is over threshold if all 40 of the leaves have living hatched mites present. The full set of mite sampling threshold tables are online.

Pyramite and Acramite are the two best options for late season mite control. If twospotted spider mites are the dominant species, then Acramite is the better option.

Japanese Beetle

Japanese beetle feeding on young trees can interfere with growth. The UMass newsletter recommends Imidan, Guthion, and Sevin as giving good control, and Asana and Danitol as giving excellent control. However, Asana and Danitol are more likely to interfere with beneficial insect predator and parasite species that help suppress aphids, mites, leafminers and other pests.

Flyspeck and Sooty blotch flyspeck on apple

Dan Cooley photo

Based on tracking leaf wetness hour accumulation, second generation flyspeck colonies were expected to have had enough time to appear starting around August 6 at Highmoor. I checked two unsprayed Liberty test blocks on Monday August 11. I found no flyspeck or sooty blotch in the first block. These are small open M26 rootstock trees, with good wind exposure and roughly 100 yards from the nearest woods. In the second block I found flyspeck colonies on 31 out of 100 fruit, and sooty blotch on 27 of the 100 fruit. The second block of trees are larger M7-sized (but not M7) trees in a low area and within about 50 feet of the woods.

Average summertime leaf wetness hour accumulation is roughly 7 hours per day (with zero LW days interspersed with rainy days of 24 hours leaf wetness). Thus, using the 7 hour average, for the first 13 days of August a typical accumulation would be around 91 hours. Actually, August is often dryer than that. But for the first 13 days of August, Highmoor accumulated 279 leaf wetness hours.

As discussed in Dave Rosenberger's article below, this extra accumulation of leaf wetness hours increases the chance of flyspeck problems appearing before harvest. The heavy rainfall in early August also depleted fungicide residues. The result is that a full-dose captan application made before August 10 could allow for flyspeck colonies to appear on fruit harvested after September 22 (which is when McIntosh is expected be just starting to reach harvest maturity). Even a Flint or Sovran application made prior to August 10 would allow flyspeck to appear on fruit harvested after October 2.

Therefore, if you haven't updated fungicide protection since the early August rains, it would be prudent to make an additional final fungicide application before putting the sprayer away. Flyspeck is normally not much of a problem in Maine orchards. But in North Carolina it is a major pest. We just had two weeks of North Carolina weather.

If more inspiration is needed, consider that while scab control has been good in most orchards this year despite the wet spring, as leaves age near and after harvest their natural resistance declines. 'Better than normal' late season fungicide protection might help prevent a late season increase in foliar scab that at the least would increase the scab inoculum level for next spring, and at the worst could spread to this year's crop.

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The following text was written by Dr. Dave Rosenberger of the Cornell Hudson Valley Lab for the August 4 Scaffolds newsletter:

"Flyspeck Flyspeck ascospores are released shortly after apples reach petal fall. On apples, the fungus requires roughly 270 hours of surface wetting time between early season infection and the time that symptoms become apparent on fruit. In northeastern United States, we are still uncertain of the exact details concerning disease development on apples. However, I believe that infection of fruit by ascospores is relatively unimportant in commercial orchards because our scab fungicides effectively protect fruit during the interval after petal fall. Ascospores are probably very important for generating new infections in woods and hedgerows that border orchards. If we assume that infections on these other hosts (of which there are many) develop at approximately the same rate as infections on apples, then those infections should also become visible and begin producing conidia for secondary infections after approximately 270 hr of surface wetting. The conidia are far more abundant than ascospores, and conidia can blow into orchards from the border areas. During a dry summer, the secondary infection cycle may not begin until early September and most infections that occur on apple fruit in September will not have enough time to develop visible symptoms before fruit are harvested. During wet summers such as the one we are currently experiencing, secondary infections on fruit can be initiated much earlier and symptoms on unprotected fruit will become visible during late summer. A wet summer may also allow multiple secondary cycles, thereby dramatically increasing inoculum that is available to blow into orchards during late summer.

Petal fall on McIntosh in the Hudson Valley occurred around 12 May this year. Peak ascospore discharge for flyspeck presumably occurred about 10 days later. Counting from 22 May, we reached 270 hr of accumulated wetting in the middle of the 91-hr wetting that occurred 19-23 June. Thus, conidia of flyspeck might have been available for infecting apples as early as late June. A flush of symptoms from those late June infections should appear on unsprayed apples within the next few days because we are nearing the completion of another 270-hr wetting accumulation (counting from 23 June). The standard recommendation for controlling flyspeck in the northeast has been a combination of a benzimidazole fungicide (currently, Topsin M is the only choice) plus captan. However, research conducted over the past several years has shown that Sovran and Flint are at least as effective as Topsin+Captan, and that in some cases they are more effective. Sovran and Flint are more expensive than the Topsin+Captan combination, but this may be a year where one or two applications of Flint in August might pay dividends, especially if one adds the potential benefits that Flint sprays may have for bitter rot control. Bitter Rot Bitter rot is a sporadic disease in northeastern United States. We have not really had weather favoring bitter rot since the early 1990's. Bitter rot can be caused by several species of Colletotrichum. Infections occur during hot wet weather and often appear as decays on the sun-facing cheek of ripening fruit. Decays are tan and slightly sunken. Slimy pale orange spores may be evident in the center of fruit lesions during wet or humid weather. In North Carolina and other southern states, bitter rot spreads rapidly and can cause major losses within several weeks if fruit are not protected with fungicide during late summer. The life cycle for bitter rot in the Northeast has not been adequately studied. I have noted the following scenarios for development of bitter rot under NY conditions: 1. Unsprayed fruit have no symptoms at harvest but develop bitter rot lesions if fruit are incubated at 100% relative humidity until they become senescent. This suggests that the fungus is often present on unsprayed fruit, but that it usually cannot cause decay until fruit become senescent. 2. The disease appears only on a few fruits near the orchard borders just prior to harvest. This occurs some years in my fungicide check plots where no fungicides are applied throughout the summer, but I rarely find more than 1-2% of fruit affected. 3. The disease may invade fruit after harvest and appear as a postharvest decay. In apple storage surveys conducted during the mid-1990's, we found that bitter rot accounted for 13% of the postharvest decays in one apple packinghouse in 1995. 4. Very rarely, bitter rot can become epidemic. This occurred in Michigan in 1995 (See Jones & Shane, Plant Disease 80:1294-1297) Annual epidemics occurred in one Long Island orchard during the early 1990's. Why does bitter rot act so differently in different orchards and different years? No one knows, but all of the following are probably factors: a. Inoculum levels probably vary greatly from year to year. In the Long Island case, we eventually discovered that horse chestnut trees (Aesculus hippocastanum) and sycamore maples (Acer pseudoplatanus) adjacent to the affected orchard were severely affected with Colletotrichum acutatum and were probably supplying inoculum for the orchard. The role of non-orchard hosts in the bitter rot cycle has not been investigated elsewhere in the northeast. b. The time when inoculum becomes available is probably critical for infections in the northeast. Bitter rot infections occur best under hot, wet conditions. If inoculum does not reach orchards until September, it may be too cool for rapid development of infections. c. Bitter rot is favored by long, warm wetting periods. Severity increases with duration of wetting up to 60 hr. In the northeast, we rarely have long wetting periods during August when temperatures are high enough to favor bitter rot infection.

So why be concerned about bitter rot this year? Extended wetting during May and June promoted bitter rot infections in non-orchard hosts. I have noted that horse chestnut trees in the Hudson Valley are already turning brown due to disease, something that has not happened in recent years. (Diseases other than those caused by Colletotrichum are also involved in blighting of horse chestnuts.) The hot, wet weather of the past week is likely to have allowed extensive dissemination of bitter rot spores in the Hudson Valley, and early ripening cultivars are already showing some evidence of infection at the Hudson Valley Lab. Only two fungicides provide good activity against bitter rot at this time of year: Captan and Flint. However, captan must be applied at the maximum label rate; half-rates will not prove satisfactory. Heavy rains can presumably remove captan residues more easily than Flint residues because Flint tends to bind to the waxy cuticle of the fruit. Thus, Flint might perform better if our frequent rains continue. Either captan alone or Flint alone should provide adequate protection against bitter rot in most orchards. However, where extremely high disease pressure is expected (e.g., adjacent to wood lots or to known source trees such as horse chestnut), growers may wish to apply a combination of Flint at the full rate plus captan at one-half of the full label rate. Neither fungicide is known to have post-infection activity against bitter rot, so timely protectant sprays are essential. Sooty Blotch, Black Rot, and White Rot will all be controlled by sprays applied for flyspeck and bitter rot. However, given the wet conditions this summer, the interval between the last spray and harvest may need to be shortened to prevent late season infections by black rot and white rot. Honeycrisp is especially susceptible to black rot and white rot, so this cultivar will need careful protection during August."

Sincerely,
Glen

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