July 22, 2015 Volume XI No. 6

Apple Summer Diseases

Flyspeck and sooty blotch we refer to as “summer” diseases of apple. The number of hours of leaf wetness after petal fall (we abbreviate this HLWAPF) is a critical factor in growth of the fungi that cause the diseases. Each cycle of the fungus requires 270 HLWAPF to complete (200 hours if you are using modern leaf wetness equipment). At UNH, we were relying on equipment that has repeatedly failed at critical times this spring. So it wasn’t until July 8 that we discovered the first 270hr cycle had been completed (in Durham) on June 28th. That means spores from the numerous alternate hosts (maple trees, raspberry and blackberry, etc) released spores starting then, and now we are in the second cycle, where those fungi are trying to grow on apples. As of July 20th, we [in Durham] had accumulated 137 hours of wetness in this second cycle. Some sites have a history of summer disease problems, probably because they have lots of nearby hosts providing spores.

Brown Rot on Peaches

Peach fruit become really susceptible to brown rot as they mature and begin to ripen. If we have warm, wet weather, that helps still more. Anything you can do to reduce mechanical injury to the fruit will help reduce the problem, and refrigerating fruit will help too. The 2015 New England Tree Fruit Management Guide lists fungicide options. Note that they vary widely in days-to-harvest… from zero to 14 days!  Yesterday I saw some nectarines that were heavily attacked by the fungus.

Fire Blight

Driving home from a tree fruit meeting in Alexandria, Cheryl Smith noted severe fireblight damage on roadside apples in a churchyard in Alexandria. Scattered strikes have been seen as far north as Lisbon this year.

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Apple Maggot

Some orchards have trapped several apple maggots by now, and others still have none. That is normal. There is great variability in the population (and timing) from site to site. Right now, I would expect early varieties (Gravenstein, Early Bird, Lodi, Vista Bella) to be most at risk.

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When you reach a cumulative average of 1 apple maggot fly per trap, it is time to apply an insecticide. If you use odor-baited traps, the threshold is an average of 5 to 10 per trap. (the big spread in range is one reason I don’t add odor lures for this species). Then, for the next 7-12 days, discount any AMF’s you happen to catch. If I’m using Sevin, I do this for 7 days, since the residue is shorter lived than that from the pyrethroid insecticides, or Guthion, Imidan. If I’m using the labeled rate of a pyrethroid insecticide (Warrior, for example), I discount for 12 to 14 days, since those insecticides have long residual action. When it is time to start harvesting a block, I move the traps to later-maturing trees. At the end of the season, I remove the traps, put them in heavy plastic bags (keeps dirt & dust out) and store them until next July.

Spotted Wing Drosophila

One point to remember regards a key alternate host: pokeweed. The fruit are excellent habitat for SWD larvae. If you grow fruit that are vulnerable to SWD, it is important to destroy pokeweed before it produces fruit. I’ve included a photo as a reminder.

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We caught our first SWD on June 23rd, a bit of a surprise that early. One was tapped in Essex Co, MA at about the same time. Finally we trapped another fly on July 8th, then at another site the next day. These numbers are really low, but should rise. In your plantings, I recommend considering an insecticide application if both 1) your crop is ripe and 2) you have trapped one or more SWD’s on your farm this year.

Details on traps, baits, how to hang, etc are on the SWD page.  The 2015 pesticide options are there as well, thanks to Mary Concklin of University of Connecticut Cooperative Extension. If you click on the trapping data link on our SWD page, you can view our trapping results, though with a slight delay. If you monitor traps yourself, you won’t have that delay.

There’s Still Time Left: Tree Fruit Leaf Tissue Testing for Nutrient Analysis

For tree fruit, leaf sampling for nutrient analysis should be done in late July through early August. The forms have the specific instructions, which can be found on the Problem Diagnosis and Testing page of UNHCE’s website.  Look near the bottom of the page, under “Additional Testing Services”. You can also download the form here.

Vegetable Insect & SWD Trapping Data

Those sweet corn growers who looked at the trapping data for the week of July 6-11 saw that we detected low numbers of corn earworms then. That is a bit earlier than we expect this pest, and is another example of the value of monitoring with traps. Sometimes you detect surprises! Numbers were not very high, but any sweet corn in fresh silk at that time was vulnerable to attack. Because of a delay getting help here on campus, we had just started setting sweet corn traps in the seacoast… but caught three earworms in the one trap we had set, in Derry. It may be that this flight was heavier along the coast, as compared to inland.

If you grow sweet corn, chrysanthemums, peppers, squash or pumpkins, and want to see the current year’s trapping data for corn borers or other insects, point your browser to our IPM Trapping and Monitoring page. Once on that page, you’ll see that one of the options is to view the current data, and it will show you how many insects were captured in traps at various sites. You could look at several weeks of data, if you wish. To help protect privacy, we don’t include farm names on the site, just the town names. On the vegetable insect trapping data pages, you’ll see that on the far right side it says “No Spray Recommended” after each entry. That’s because we want to keep the spray recommendations private as well. Look at the very bottom of the page as well. There you’ll see the threshold information, to help you decide what to do when a particular number of earworms or other insects are caught. The data is ready for you to examine any time you wish, for sweet corn & squash trapping. As I finalize this on July 21st, we have caught a few fall armyworms… not too many yet.

Summer Caterpillars

On apples, we see two large caterpillars regularly, in summer. Both can completely strip leaves off a limb or two, or even the whole tree. Both are highly recognizable. Cecropia moth is one of our native silkworms, and the larvae are light green with a series of colored spiny knobs. They can get HUGE.

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The second species is called redhumped caterpillar, and you can see why from the photo. This species is gregarious; you almost never have just one. The female lays eggs in masses, while cecropia moths lay their eggs singly.

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In blueberries, we often see two very closely related species, yellow-necked caterpillar and its look-alike, Drexel’s datana. Like red-humped caterpillar, they are gregarious species, and a bush might get largely stripped of leaves if you don’t keep checking.

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All of these species can be controlled (if that’s necessary) by either chemicals or Bacillus thuringiensis sprays. Since most of our blueberries are sold on a pick-your-own basis, and the caterpillars occur during picking season, many blueberry growers avoid using the chemical sprays. Some growers spray nothing, and when customers mention finding the caterpillars, the grower points to it as proof that he/she doesn’t spray.

Fruit-Related Events:

There are many events that might be of interest on our events calendar. Among them are:

Tuesday, July 28, 2015. Sprayer Calibration & Vegetable Twilight Meeting, Moulton Farm, Quarry Rd, Meredith. The sprayer calibration workshop is 3 to 4:30PM; Veg meeting will be 5:00 to 7PM

Alan T. Eaton
Extension Specialist
Integrated Pest Management

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