August 25, 2015 Volume XI No. 7

Apple Summer Diseases

 Apple Maggot

All varieties of apple are vulnerable to attack by apple maggot, but my fruit evaluations over the years have pointed to a pattern where some varieties get more damage than others. This could be in part because of preferences of the females laying the eggs. But it could also be affected by growers’ pattern of insecticide use… not using traps to discover when the flies are active, stopping spraying too soon, beginning too late. So, keeping those factors in mind, here’s my data from 1996 to 2005. In that period, I examined 119,500 apples. These are visual examinations. No fruit were sliced open to search for tunnels.

Variety                        incidence of AM blemishes

McIntosh                   18 of 50,740 fruit (0.035%)

Cortland                    33 of 29,000 fruit (0.114%)

Delicious                   27 of 12,430 fruit (0.217%)

Idared                        4 of 420 fruit        (0.952%)

Northern Spy            3 of 670 fruit        (0.448%)

Gingergold                1 of 320 fruit        (0.312%)

Gravenstein              1 of 340 fruit        (0.294%)

Empire                       7 of 5,040 fruit     (0.139%)

Macoun: 0 of 7,830 fruit. Paulared: 0 of 2,600 fruit. Gala: 0 of 2,650 fruit. Mutsu: 0 of 1,560 fruit. Honeycrisp: 0 of 1,010 fruit. Plus other varieties in small amounts…

The mix of varieties we grow has changed, and now I see more Gala, Mutsu, Honeycrisp, Fuji, Gingergold, Zestar, Akane and other varieties. But for what it’s worth, this is the pattern I’ve seen. Note that McIntosh, the variety that has the largest acreage here, has among the lowest apple maggot damage rates. Cortland has a damage incidence three times higher than McIntosh, and Delicious has an incidence 6 times higher.

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White Apple Leafhoppers

We have two generations of white apple leafhoppers per year, and the adults of the second generation fly in September. The nymphs and adults both drop brown poop on whatever is below them, like your fruit, or the insect trap in the photo. When we get a light rain, heavily decorated fruit appear to be dripping in yellow droplets…not too appetizing. The leafhoppers feed on the foliage, creating white stippling. But many growers feel the most annoying problem is bothering pickers by flying in their faces. So some growers elect to apply an insecticide if leafhopper numbers get high. You can do that, but a better course of action (next year) is to monitor the first generation of leafhoppers (shortly after petal fall) and treat then if the population crosses the threshold.

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Vegetable Insect & SWD Trapping Data

So far this year, sweet corn insect catches have been pretty low, but you can see the details yourself at the IPM Trapping & Monitoring page of our website.

Spotted Wing Drosophila

The catches Aug 1st to 7th were mostly 0-4 per trap, with a couple sites having 30. The week of Aug 2nd to 9th had a similar pattern, with catches up to 42 in a trap, especially in woods edge and in raspberries or plums. The week of Aug 9th to 15th had the same pattern with some catches as high as 60! But again, Most traps still have low numbers.

In Sullivan and Grafton counties, SWD catches are still very low, typically zero to 3 per trap per week. This is the same pattern we have seen since SWD arrived… the areas with cooler temperatures have slower buildup and lower numbers. Overall, New Hampshire catches so far seem lower than last year, but they should continue to build. You can view our trap catches on the IPM Trapping & Monitoring page of UNH Cooperative Extension’s website. When you reach the SWD data, click on the town that is of interest to you, and various weeks will appear under that town. Select the week of interest, then click on the “submit” button. The data will then be displayed for that site & week.

Wasp Control on PYO Farms

Stinging wasps can be a threat to both customers and farm workers. Late summer and early Fall seems to be the time of year when the threat is greatest. The wasp colonies are at their largest size then, and sometimes frost starts limiting food options for wasps. I suspect that might help switch them into a more aggressive pattern, but I really don’t know. I do know that it is better to deal with the problem relatively early, if you can. We have 11 pretty aggressive species in New Hampshire, including 9 species of yellow jackets, plus bald-faced hornet and giant European hornet. We also have species that are much less aggressive, like brown paper wasps. Frequently the less aggressive ones pose so low a risk, they can be left alone.

Please remember two things. 1) If you are allergic to bee/wasp stings, do not attempt to eliminate a nest yourself. Have someone else do it. 2) During the daytime, mark the position of a nest you want to eliminate. Then return at least 1 hour after dark, to treat it. Why at night? All of the workers should be back in the nest then.

Consider buying a can of wasp and hornet JET spray. Jet is not a brand… it means the stuff is designed to shoot a solid stream of product, often up to 10 feet or more. I would not bother to try the canned sprays that create a fine mist. .Approach the nest gently, quietly. Aim directly into the opening. This might mean positioning the spray can a bit below an aerial nest. I use a red light to help me see what is going on. After hitting the opening for several seconds, stop and walk away. Stay away until the next day. If you still see wasps flying in or out, re-treat the next night.

Large aerial nests are fairly easy to find by their size. Nests inside walls or in the ground are much harder to spot. To find them, I look for insects flying into or out of a hole. I do one additional thing when treating a ground nest. In addition to the flashlight and spray can, I bring along about a quart of damp sand. As soon as I have stopped spraying, I dump the sand over the entrance tunnel. That helps seal in the toxicant and prevent wasps from escaping.

One contributor to the problem may be a bit hard for you to control: wasps are attracted to dropped fruit and spilled sugary things (like cider). Removing drops is often impractical, but it works. Here is a link to my publication on controlling wasps.

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Flyspeck and Sooty Blotch of Apple: As of August 17th in Durham, we have accumulated 295 hours of leaf wetness since the end of the first 270 hour cycle. So that means the second cycle ended on August 12th and spores started getting released. As of Tuesday morning Aug 18th we are 25 hours into the 3rd cycle of flyspeck. Remember to check the days to harvest if you apply a flyspeck fungicide. Manzate, Dithane, Polyram and Penncozeb have a 77days to harvest interval! Sovran has a 30 day interval, while others have 14, 1 or zero.

Alan T. Eaton

Extension Specialist

Integrated Pest Management

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