April 9, 2015 – Volume XI, No. 2

Fertilizer and Other Factors Affecting Gray Mold on Strawberry

We have several non-chemical steps we suggest to manage gray mold (Botrytis) problems on strawberries. The fungus attacks both foliage and fruit, and is encouraged by wet conditions and warmth. In a December meeting, I was reminded that research at Cornell University demonstrated that excess nitrogen fertilization early in the growing season results in elevated Botrytis problems on strawberry fruit that season. From both research and experience on farms, we know that keeping rows narrow helps reduce gray mold problems, by reducing drying time. Most growers rely fairly heavily on fungicides, so you know that we recommend starting applications during bloom (early bloom for many), since gray mold often starts up on petals. Removing dead foliage from the crop would help, but might be a very expensive (labor) cost.


How Are The Pests Surviving The Winter?

The media reported that Concord NH had the coldest February on record. I was immediately asked how the insects & ticks would survive. That depends a bit on what the “coldest” means, and which insects are of interest. I assume the “coldest” means that the average temperature was the lowest on record. But that may not say too much about how survivable it was for insects. For many insects, there is a critical cold point below which they cannot survive. If we reached that point one night, and the rest of the winter was relatively mild, then insect survival would be lower than if we had a winter where the average temperature was much colder, but it never reached the critical low point.

European red mite eggs

European red mite eggs

Another factor is where the insects overwinter. For those buried under two feet of insulating snow, survival may be very good. For eggs laid on twigs in the open (like European red mite eggs in the photo above), they experience the full brunt of the exposure…wind, cold temperatures, all of it.

So, blacklegged ticks, apple blotch leafminers, tarnished plant bugs, two-spotted spider mites, and apple scab fungus should survive our “coldest February” very well. I anticipate lower survival than usual for European red mites, Eastern tent caterpillars, Hemlock woolly adelgids, and others that are fully exposed. For those that are partially protected, like codling moth, lesser appleworm, Typhlodromus pyri (predator mite), the answer is somewhere in the middle.


2015 New England Tree Fruit Management Guide is Here

This time it is 284 pages, and costs $35. I’ll bring some copies to the tree fruit twilight meeting on April 22 at Sunnycrest Farm in Londonderry. Catch my administrative assistant if you’d like to get one before then. 862-3200


More on Bee Toxicity

In addition to Clothianidin, imidacloprid and thiamethoxam that I disussed in the January issue, other agricultural chemicals are highly toxic to bees. On the highly toxic list are Sevin and Lannate; the organo-phosphates Diazinon, Imidan, Guthion, Lorsban, Dimethoate and Malathion; the synthetic pyrethroids Ambush, Asana, Baythroid, Brigade, Decis, Danitol and Warrior; the IGR Rimon; the macrolactic lactones (say that 3 times fast) Agri-mek, Proclaim, Delegate, and Entrust; and the miticide Pyramite. Formulation is a consideration. If you had the same chemical in various forms, the dust formulation would offer the greatest bee hazard, followed by wettable powders, flowable powders, then emulsifiable concentrates and granules.

There is a new symbol (a honeybee) on the labels of new insecticides that are significantly toxic to bees. I’m expecting to see this on more products, as older labels get upgraded.


Early Season Tree Fruit Pest Events

Some insects overwinter as adults, and are all ready to emerge & feed if the opportunity occurs. Tarnished plant bug and pear psylla are in this situation. If we get a warm spell after the snow has melted, we sometimes see activity of these two species. Typically 60F or higher plus sunshine triggers their activity. Some insects are closely tied to the opening of buds on which they rest. Apple sucker is one example. Each overwintering egg of apple sucker has a tiny probe inserted into the bud or twig, and it seems to detect when bud break occurs. That’s why it is really closely tied to bud break. On apples, caterpillars of green pug and eye-spotted bud moth appear shortly after the buds open. Winter moth eggs are also relatively early to hatch, and you might find them on apple, blueberry, maples or oaks.

Peach leaf curl

Peach leaf curl

Some pathogen events are tied to bud development stages because they are critical windows for controls. One example is peach leaf curl. The disease can be managed by certain fungicides (Bravo, C-O-C-S, Echo, Ferbam, Kocide, Badge, Ziram…) but only if they are applied at the correct time. Generally, that’s between leaf fall and bud swell. Sprays made shortly after buds started swelling might provide partial control.

Lime sulfur applications on brambles are unsafe after about ¼ inch green stage, because they can burn the opening tissues if applied too late.


Early Season Tasks for Orchards With Fireblight

If you had fireblight in your orchard last season, Cheryl Smith suggests that you consider applying an early copper spray. It is usually done when buds are dormant. If you delay until after ¼ inch green, you risk getting phytotoxicity. The copper spray kills most fireblight bacteria that are exposed on surfaces, and it reduces the chances of getting strikes this season. If you are still pruning AND THE TREES ARE STILL DORMANT, you don’t have to sterilize shears after every cut. Maybe our buds will finally break before July.


Impacts of the IPM Program

I recently completed a video (a power point presentation with an audio track) that covers the impacts of UNH Cooperative Extension’s IPM work. Originally it covered the history of the IPM work as well, and had photos of some of us from 20 to 35 years ago. But that was too long, so this version is shorter than 8 minutes. In particular, it measures impacts from 2013, the most recent year for which we have completed impact data. We found $1.4million in impacts, just in the areas that we could easily measure. Got time during lunch? Follow this link & view it yourself: http://extension.unh.edu/Impact-Videos


Alan T. Eaton
Extension Specialist
Integrated Pest Management


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