July 2, 2014 – Volume 10 No. 5

Apple Scab

Now that we are in the secondary scab season, disease spread is from splashing of conidia, which form on the lesions. It is common to have a lesion or two high in a tree top, and have new infections result from rain splash around and below those primary lesions. Conidia get spread either during the day or at night. This is different from the pattern during primary season. The ascospores that cause primary infections are released by DAYTIME rains. Almost none get released if the rains come at night. So the good news is: now you can worry day AND night.

Fire Blight

During the week of June 8th, it became clear that we had several orchards with lots of fireblight strikes. The symptoms take quite a while to appear visually, after the infection event. Some orchards have lots of affected trees, with multiple strikes per tree. There are several possible actions for growers to consider. One is to leave it alone for now, and if a hail storm hits, apply streptomycin within 24 hrs. Another is to prune out all of the FB strikes at least 6 inches below any visible symptoms. This must be during dry weather, and you must wipe the pruners with 70% alcohol between each cut. George Hamilton reminded me that wiping is much more effective than dipping. You might do the ugly stub method, leaving an ugly stub to be pruned out during dormant season. If the trees are really heavily hit, you may just choose to cut them down, since they may die anyway. Fireblight-susceptible apples and pears should get a streptomycin spray within 24hours after being hit by hail, even if you don’t see any fireblight strikes.

Rose Chafer, Oriental Beetle & Japanese Beetle

These three related beetles all cause defoliation of various tree or small fruits, and some feed on the ripe fruit as well. Rose chafer is the first to appear, usually the latter half of June. The adults are active into perhaps mid-July. The beetles are tan, with long, spiny, spindly legs. They especially like to feed on foliage of grapes and brambles, but can be found on pome and stone fruit as well. They are more common in regions with relatively sandy soils. Usually they don’t occur in numbers high enough to be a serious problem. Larvae are white grubs that feed on plant roots.

Rose chafer

Rose chafer

Oriental beetle is a relative newcomer. The pattern of dark and light patches on its back varies quite a bit. Adults are active from about June 28th until sometime in August. They feed on leaves from a very wide range of species. I don’t see it eat fruit very much. The immatures are white grubs that feed on roots, especially grasses.

Oriental beetle

Oriental beetle

Japanese beetle is familiar to most NH growers, and in Northern Grafton, Carroll and Coos counties it has recently increased in numbers. In Rockingham county, the first shiny green & brown adults appear about June 30th. For the rest of the state, that happens in July. Numbers peak in the second half of July, and a few are still feeding in late September. They feed on a huge range of plant species. In addition to leaves, they really like ripe fruit. They can heavily defoliate grapes, brambles, stone fruit and some apples (Honeycrisp for example). I sometimes see them feeding on blueberries or strawberries as well.

If the damage gets serious, there are insecticides to protect the fruit. If you are an organic grower, Surround can be reasonably effective at protecting foliage, but you have to use more than one application to get good coverage. I’m a little shy about widespread Japaneese beetle spraying in apples. Several years back, we triggered a major outbreak of woolly apple aphids at the UNH Woodman farm, by spraying Sevin for JB. Today, I might consider spot spraying only those rows that are seriously hit (like Honeycrisp) if JB is a problem. Why did the spray cause an outbreak? Sevin is a broad-spectrum insecticide that is especially rough on Hymenoptera. Woolly apple aphid numbers are significantly controlled by a tiny parasitic wasp, in the order Hymenoptera. It appears that our spray was at exactly the time when the parasites were active, and most got killed. It took several years for the woolly apple aphid numbers to return to “normal”.

Slugs in Strawberries

In years with relatively wet, humid June and July, slugs can be numerous. They feed on foliage and fruit, especially at night. On humid days, they are active during the day. On dry, hot days, they take cover under mulch or in other protected spots. A mulched, matted row of strawberries is just ideal for them. There are some slug-killing treatments (Deadline and Sluggo for example), but they usually don’t work really fast. We usually suggest using them early, if a problem develops. You need to avoid contaminating the fruit, so application during harvest can be problematic. We have several species of slugs here, and the toxicants seem to work on all of them.

Black Vine Weevil: Serious Strawberry Pest

What an unusual insect this is! All individuals are females. They reproduce without the need to find a mate. Adults are photo-negative; hiding in debris during the day, and feeding at night. In years with very mild winters, some adults can survive the winter, though that’s not very likely in most of New Hampshire. We actually have three very closely related species here. The largest and most destructive is black vine weevil. A very close relative, the rough strawberry root weevil, is a slightly smaller version of black vine weevil. You need a microscope to tell the species apart. This one isn’t very common here. The third species is the smallest and is probably the most abundant.

All three have virtually identical life cycles, which begin with eggs laid in the soil in August. Eggs hatch into tiny, white grubs that have no legs. They feed on the roots and crown through the fall, and resume feeding when the soil warms in the spring. They are fully grown by early June, and pupate in the soil. Then the first adults appear around the end of June or early July.

One sign that a strawberry bed is infested is that the plants look a bit weak, and fruit flavor is poor. A more obvious sign is leaf notching. Adults chew holes only from the edges of the leaves (at night of course). If you see significant leaf notching, clear away some of the leaf litter and see if you find an adult or two.

Controlling this species is difficult. We have no treatments that quickly knock down their numbers. You could try Brigade, which will kill some of the adults. But many survive, and using that material tends to eliminate predator mites, thereby creating two-spotted mite problems, which then must be attacked with more sprays. Insect-killing nematodes can work, but they would not be applied now. Early May or September is the time for that. There are some new insecticides (Platinum, for example) that might (?) kill the young larvae, but they would be applied in fall or early spring.

Weevil leaf notching

Weevil leaf notching

If you have a serious problem, the scorched earth policy really helps: 1) Destroy the old bed thoroughly, by disking the bed after harvest. 2) Plant a new bed as far from the old one as possible, preferably at least 100 yards. 3) Where the old bed was, plant some other crop on which black vine weevil larvae cannot survive, and have no BVW-susceptible crops there for at least two years. 4) After two years with no BVW hosts, it should be safe to re-plant strawberries. Check the host species list below…there are some common weeds on it.

Another tactic works, but is difficult logistically: you could plant a new bed relatively close by if you immediately surround it with a “fence” as soon as it is planted. The fence consists of 1 foot high polyethylene, supported by stakes (on the interior side), and firmly embedded in the soil. BVW would re-infest by walking into the bed, and the plastic is too slippery for them to climb. This has been demonstrated by research, but the logistics are almost impossible: if you drive a tractor or other implement over the fence, you must repair it quickly. Some growers here have tried this, using a fence of tar paper, with a sticky material (tangle trap) in a two-inch band at the top of the outside surface. That worked well for a while, until soil covered the sticky surface. On one really hot day, tangletrap melted and slid down the tar paper, and had to be re-coated.

Black Vine Weevil Host Species

Achillea, Asters, Astilbe, Azaleas, Begonia, Bergenia, Blackberry, Calla lily, Cinquefoil, Cyclamen, Dandelion, Dock, Epimedium alpine, Epimedium grandiflora, Adiantum fern, Christmas fern, Hemlock, Heuchera, Hosta, Hydrangea, Impatiens, Isoloma, Lily of the Valley, Lythrum, Mountain-Laurel, Phlox, Physostegia, Plantain, Primrose, Raspberry, Rhododendron, Rhubarb, Sedum acre, Strawberry, Sheep sorrel, Wood sorrel, Taxus (yew).

SWD: Expect First Adults Soon

I’m expecting that the first adults of spotted wing drosophila will appear in traps roughly July 1-10th. That’s just the very first ones. Numbers will build up steadily. If you grow vulnerable fruit (brambles, blueberries, cherries, plums, peaches, day-neutral strawberries, grapes…) I suggest that you put out a couple (or more) SWD traps when the fruit turn color. Details on traps, baits, how to hang, etc are on UNHCE’s website on the Spotted-Wing-Drosophila page. We may update the SWD pesticides list again. Did you see my note earlier, about a new pesticide, called Exirel?

Blueberry Fruit Fly and Apple Maggot

Adults of these species begin flying about July 1st. For blueberry fruit fly, the peak flight (and attack time) is the week of July 13th. For apple maggot, peak attack varies greatly, but usually is in August. Red sticky sphere traps are best for AM; the Trece (yellow cardboard) AM traps work best for BFF if they are hung in the V position. Details on BFF trapping are in the Using Traps to Monitor Blueberry Fruit Fly in New Hampshire fact sheet George Hamilton and I wrote.

 

Eatonsiggif

 

Alan T. Eaton, Extension Specialist, Integrated Pest Management

 

Visit the Extension IPM page.

 

UNH Cooperative Extension programs and policies are consistent with pertinent Federal and State laws and regulations, and prohibits discrimination in its programs, activities and employment on the basis of race, color, national origin, gender, religion, age, disability, political beliefs, sex, sexual orientation, or veteran’s, marital or family status. New Hampshire counties cooperating.

 

 

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