April 28, 2015 – Vol. XI No. 3

Bud Stages

On Monday April 20, almost 50% of the McIntosh apple buds in Durham/Lee were at silver tip and 50% were at early green tip. Peach buds were almost all dead. Blueberries were all swelling. Raspberries showed about ¼ to ½ inch of growth. On Wednesday 22nd, McIntosh buds in Derry & Londonderry were mostly at ¼ inch green stage. There were lots of peach buds swelling.

On Monday April 27th, 95% of McIntosh apple fruit buds in Durham/Lee were at the half-inch green stage.  There were many more live peach buds than I thought earlier.  Blueberry buds were swollen (tight scales), and raspberries showed ½ to 1 inch of growth from the buds.

Setting up Traps for TPB & Leafminers in Apples

If you monitor tarnished plant bugs in your apples with white sticky rectangle traps, the time to hang them up is at silver tip stage. If you have passed that stage, it is too late to get an accurate assessment of TPB numbers. The traps are mimics of a cluster of opening foliage (works on the TPB’s anyway), so they should be hung towards a branch tip. Also important: hang them at knee height, over a grassy (not bare) part of the orchard floor. IMG_1769

Are you monitoring leafminers? The red sticky rectangle traps for those go up at ¼ inch green stage. They get stapled to the south or southeast side of the trunk, at knee height. As with TPB traps, you check them every week and write down the numbers caught. I’ve had growers ask me if they could stretch out the interval, and check after 10 to 14 days. I don’t recommend that, because the trapped insects gradually turn black, and get very difficult to identify if they’ve been caught a long time.

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Recognizing the catch is relatively easy for both. Leafminer moths are narrow, about 3mm long (slightly over 1/16 inch). Their wings are bright silvery white, with dark markings. Overwintered tarnished plant bugs are dark, almost black, and shield-shaped. They are 4 to 5mm long (almost ¼ inch), with long, thin antennae.

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Threshold for TPB’s in Apples

If you have a good market for #1 fruit (like PYO blocks), a cumulative catch of 5 TPB’s caught per trap from silver tip to tight cluster makes it worthwhile to spray. If you haven’t reached threshold by tight cluster stage, wait and look again at pink stage. A cumulative average of 8 or more per trap by pink would warrant control. For apple growers who aim to produce extra fancy apples, the thresholds are a cumulative catch of 3 per trap (ST to TC) and 5 per trap (ST to pink). Many apple growers don’t bother to spray for TPB any longer. I think that’s great!!

Threshold for Leafminers on Apple

The traps are very effective to predict whether or not you need an insecticide this year for these pests. Threshold varies with apple variety. For McIntosh, it is a cumulative catch of 4 or more moths from quarter-inch through tight cluster stage. For other varieties, the threshold is 9 or more moths, because other varieties are much less sensitive to leafminer damage.

Insecticide Options for Leafminers on Apples

Once you have determined that you do need to control leafminers this year, There is a really wide range of insecticide options & times.

1) Insect growth regulators (Esteem and Intrepid for example) are most effective on eggs and very young larvae, so if you need to spray, and wanted to use them, spray at late tight cluster (pre-pink) or pink stage. Organic growers don’t usually have leafminer problems, but if they do, Aza-direct is OMRI listed, and would be used then.

2) Vydate is an organophosphate insecticide, rough on beneficials, but effective on leafminers. The preferred timing for that would be at pink, because spraying Vydate soon after pink can cause erratic fruit thinning.

3) Materials that are effective on the young larvae (sap-feeders) come next. That should be soon after petal fall. Proclaim is one example. You use it with a surfactant, and it has some translaminar (foliage penetrating) action. Exirel is a new one that would be used at that time. Gladiator and Tourismo are both relatively new combination products that would be used then. The Voliam flexi and Actara labels have similar language — apply right after petal fall. Other labels say just during the sap-feeding stage, so that could be a little bit later (watch for signs on your leaves). Agri-Mek, Altacor, Assail, Belt, Calypso, Delegate, Lannate, Leverage, Provado, Entrust and SpinTor are in this category. Some Insecticides require a surfactant or horticultural oil be added to the tank, to penetrate properly and be effective. Be sure to check the labels!! Agri-Mek, Delegate, Agri-Flex and SpinTor are in this group that need to be tank mixed with a surfactant or oil.

4)  We have a number of pyrethroid insecticides that also work on leafminers. I believe they affect adults (or eggs, if you have high enough gallonage to hit them), not the immatures, which are inside the leaf layers. Pyrethroids (in general) are quite persistent and broad spectrum, so they can be very harmful to beneficial insects. I downplay them as an option for leafminers. Examples include Asana, Baythroid, Delegate, Warrior.

Label language: Avaunt is registered to suppress leafminers, which to me means it doesn’t work too well. Watch out for this phrase. Repeat sprays: If you apply an insecticide for this generation of leafminers, you should need only one treatment. If you treat (correctly) for the first generation, it would be rare to require a leafminer treatment later in the season. Later in the season, if you do find out that you need to treat for leafminers, generally it would take two applications to provide control, while controlling this first generation would require only one.

Apple Scab Update — Cheryl Smith

SARE project collaborators are still monitoring ascospore maturity in New England. Massachusetts people are doing petri dish and squash mounts (a graduate student project). In New Hampshire and Maine, spore trapping is going on [MacHardy, Smith, Schneider]. We will know the actual start and true end of the ascospore season. In Durham on April 20th, 45% of the McIntosh buds were at green tip stage. By April 22nd, it was probably over 80%.

There is now a NEWA weather station in Hollis. The model says there was an infection period Monday-Tuesday. It was wet long enough, though cool. Only 3% of the ascospores were mature, but we don’t know how many (if any) got released. In Durham, there were none trapped. The Durham weather station showed 39 Apple scab ascospore degree days accumulated since 4/15, but the 15th was before our biofix. Soooooo, very southern NH may have had an infection period. The scab model on the NEWA website (for Hollis NH) estimated 3% of the ascospores were mature, and we had an infection period then. It predicts 15 days (after the Mon-Tues wetting period) for any symptoms to show up. If you have blocks of apples that you are SURE have very low inoculum (urea spray, leaf-chopping, or passed a PAD count in the Fall) you don’t need to worry about a few percent of spores being mature (prob. below 8-10%). But, if you’re not sure, it would be wise to be covered before the next significant rainfall (the next infection period). If you are beyond green tip stage and are not covered, it may be good to apply a kickback fungicide. Check Alan’s Fruit pest update telephone (862-3763). I or Bill MacHardy or Deb Schneider will be giving spore maturity info.

Cedar-Apple Rust — Cheryl Smith

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We had lots of cedar-apple rust [CAR] in 2014, with great jelly horns visible. So far, no horns are visible on galls, but they will begin releasing spores soon (during rainy periods), through May. Leaf spots should be visible by June. Some varieties are really susceptible, such as Braeburn, Fugi, Gala, Ginger Gold, Golden Delicious, Idared, Mutsu, Rome, and others. Remember that the best management practices for CAR are to grow resistant varieties, and separate apples from the alternate hosts, redcedar.

Oil for Red Mite Eggs

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The easiest time to smother mite eggs with oil is when they are respiring the most rapidly. That occurs just before they hatch, so the ideal time on apple is during the tight cluster stage. In the past I’ve shown tentative sampling procedures and thresholds for ERM eggs in early spring. But I’ve found no one that used them. I’ll offer some added, easy guidance: If you have a block where your pruning gloves got orange streaks after handling the branches, that’s a block to be sure you treat with oil. Some growers have so much acreage to cover, that they have to begin before TC stage. You want to get this treatment done before pink stage, because that’s when the eggs start hatching, and the motile mites can just walk out of the oil.

Be careful about temperatures, when applying oil on apples. Try to apply it when the temperature won’t dip down into the 30’s within 24 hours of application. Also, don’t mix it with Captan, and don’t use Captan as the next fungicide after applying oil. Getting Captan and oil too close (or mixing them) results in brown phytotoxic spots on the foliage.

Winter Moth Update

There is very little risk of winter moth injury here in NH, except in southeast Rockingham County. But we do have another species that is very closely related, with nearly identical biology, which hybridizes with winter moth. So you might experience problems from a very early season, green looper that chews holes in foliage. Damage is worst on oaks, maples, blueberries and sometimes apple, especially bordering woods. The moths lay eggs in late fall and early winter, in bark crevices of trees. Winter moth eggs hatch very early, as buds are swelling and beginning to open. One odd quirk: the (orange) eggs turn blue just before they hatch!  When we see problems, it is usually due to a gradual buildup, rather than sudden appearance of a problem. Yes, chemical insecticides work on the caterpillars, but so do biological insecticides like those based on the caterpillar strains of Bacillus thuringiensis. Trade names include Dipel, Biobit, Deliver, Javelin. Timing? Often that’s pre-bloom.

Stem Galls on Blueberry

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I received these galls just after the last newsletter was issued. They were created last year, by a wasp named Hemadas nubilipennis Ashmead. No, there is no common name, but you could call it blueberry stem gall wasp, and entomologists and blueberry growers would both understand you. I see these mostly on wild and backyard blueberry bushes. The adults are tiny black wasps, and they fly in June or early July. If you see old galls in mid-summer, with tiny holes in them, the wasps have already emerged. If there are really high numbers of galls on a bush, they can reduce fruit production. That is rare, by the way.

In my backyard, I prune these out during the dormant season, and burn them. If you see low or moderate numbers of them, I wouldn’t worry. The species is heavily parasitized by other wasps, and that may be one reason that I rarely see high numbers of these galls.

Girdled Grapes

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I pruned my grape vines before the snow had fully melted. A week later the rest of the snow melted, and revealed that both vines had been girdled by voles over the winter. I asked George Hamilton if some latent buds might break below the girdle point, and save the vines. He said that might happen, so I’ll wait and see. In the meantime, there is a lesson. Meadow voles are the most common cause of this girdling, and two things made it more likely for this problem to occur. One was that I did not keep the weeds down under these vines. The other is that the previous owner had piled small rocks (4″ to 9” in diameter) under the vines and bordering the entire garden. I guess this was to create a visual border. Meadow voles really like both situations, because they get protected from most of their enemies by thick grass or weeds, and rock piles. When the snow fully melted, I found a vole nest only 3 feet from one girdled grape vine, and another nest 5 feet away. I suppose I could have installed vole (“mouse”) guards of ¼ inch mesh hardware cloth around each vine. But George sent me photos of one vineyard where the girdling was very high on the plant. It would have been difficult to construct guards to prevent that. My future efforts will be on removing the rock piles, and keeping weeds controlled or mowed.

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Brown Rot on Stone Fruit — Cheryl & Alan

Brown rot hits our stone fruit, and is most favored by rain and cooler temperatures during bloom. Removing mummies from the trees will help in managing this fungal disease. Insect control can help, too, by eliminating insect injury on the fruit as a point of entry for the fungus.

Alan T. Eaton
Extension Specialist
Integrated Pest Management

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