Tag Archives: eastern tent caterpillars

April 18, 2017 Volume XIII No. 2

Fruit Bud Stages

In the Durham area, McIntosh and Cortland apple fruit buds are mostly at half inch green stage, with a few buds still at quarter inch green. Peaches are at pink stage, with a few buds still at half inch green. Blueberry fruit buds have loose scales, with one variety at early tight cluster. Raspberries show ½ to ¾ inch of growth from the fruit buds.

Apple Damage Photograph

The photo used for the header in this year’s newsletter shows a certain type of injury to apples. Can you tell what it is?  I’ll reveal the answer later in the season.

Tarnished Plant Bug

A few growers still monitor for tarnished plant bug, using the white sticky rectangle traps (still available from Great Lakes IPM). The traps can tell you whether or not it is worthwhile to apply an insecticide for this insect. Place the traps at knee height, towards the tip of a low branch. Yes, that’s at KNEE height. The trap should be over a grassy (not bare) part of the orchard floor. I tend to hang them relatively close to the orchard periphery, but that’s not essential. When?  Hang at silver tip stage. Then you check them weekly and count (then remove) any tarnished plant bugs you catch. Some growers use these to compare differences block-to-block. I’d expect more TPB injury in a block that was adjacent to hay fields or clover, compared to one that was surrounded by woods.

There are several thresholds. For people with a strong market for #1 fruit (like pick-your-own growers), it is worthwhile to apply an insecticide for TPB if the cumulative catch (from silver tip to tight cluster stage) per trap is 5.5 or more by the time of tight cluster. If you haven’t reached that threshold by TC stage, keep the traps up and check again at late pink stage. The cumulative threshold from ST to late pink is 8 or more per trap.

If you are aiming for extra fancy fruit, the threshold is from ST to TC is 3.5 per trap, and ST through late pink is 5 per trap.

Identifying the insects: tarnished plant bugs are 3/16 inch long, with long, thin antennae. Overwintered adults are dark brown. The body is shield-shaped.

Monitoring Leafminers in Apple Orchards

We have two species of leafminers that are difficult to tell apart… apple blotch leafminer and spotted tentiform leafminer. Both can cause premature fruit drop, usually just as you are setting out bins in your McIntosh block. McIntosh is the variety most sensitive to this injury. We can monitor populations of these leafminers by two methods: red sticky traps or counting the tissue-feeding leaf mines. If you choose to use the traps, they need to go up soon. The red sticky traps are available from Great Lakes IPM www.greatlakesipm.com I’d place them in blocks where leafminers have been a problem in the past. Attach one at knee height to the south side of the tree trunk. Some growers use a stapler for this, while I use four push pins. When do you set them up?  Do this at green tip stage. Sometimes you can delay until ¼ inch green. The moths start emerging just after QIG stage, and you check the traps weekly for the tiny moths. Don’t check your traps over a longer interval than 1 week, or the insects will turn black and you won’t be able to identify them. Count and remove the moths each week. The moths are almost 2/16 inch long, with dark silvery marks on white, elongated wings.

In a McIntosh block, the threshold is 3-4 moths or more by early pink stage. In all other varieties, the threshold is 6-8 or more by early pink stage. If the leafminer population is below the threshold, I suggest that you NOT spray an insecticide for them.

These thresholds tell you IF it is worthwhile to apply a leafminer treatment. WHEN you treat is up to you. You have 2 generations that could be targeted, with multiple windows of opportunity before mid-summer. Generally, treating for the first generation is more effective than the second, because it is more synchronous than the second. I NEVER recommend treating for the 3rd generation, because it is too late to prevent the fruit dropping, and the third leafminer generation is heavily parasitized by tiny wasps.

Winter Moth

Winter moth eggs hatch when the buds are opening, and the tiny caterpillars sometimes balloon into the edge of your orchard or blueberry planting, from adjacent oak or other trees. They are not very difficult to control, but timing is important. If your blueberries/apples are in the seacoast region, you have a greater risk of a problem than people who are located farther inland in New Hampshire. Make a note on your calendar to check for these insects, especially at the edges of your planting.

Eastern Tent Caterpillars

Eastern tent caterpillar eggs are in a shiny mass that usually encircles a twig. I rarely see them in conventional commercial orchards, but they are very common in organic blocks and backyard trees. Apples, cherries, peaches and pears seem to be the most frequently attacked. The insects are easy to control (even with Bacillus thuringiensis), unless you wait until they are huge. For many years I could accurately say that they hatched about April 15th. In recent years, it has been significantly earlier. The tiny caterpillars feed on the leaves, and begin to construct a silk tent in a nearby crotch. In most orchards, they are controlled by insecticides directed at other insects. If you see the egg masses before they hatch, you can avoid damage to your tree by removing and burning the egg masses. Just peel them off the twigs. My photos show an egg mass in early March and some very young ETC caterpillars in April.

Apple Scab

The biofix (starting point) for the apple scab fungus spore maturation model is when 50% of the McIntosh buds have reached green tip stage. Really early in the season, there is relatively little host tissue that is exposed, and a small % of the season’s supply of spores that are ready for release. As the season progresses, more vulnerable tissue is exposed. Typically we have the largest spore releases around the period of pink or bloom stage. Then, the primary infection season winds down, often in early or mid-June. It ends because the ascospore supply gets exhausted, and the dead apple leaves from last year are breaking down. But the lesions that result from primary infection enlarge and start producing infective spores called conidia, which get spread by rain splashing. So we can have many cycles of the disease by the time the season ends. If growers get through primary season with few or no lesions, they can relax spraying quite a bit (for scab anyway) after that.

So, we are at the beginning of primary scab season, and growers need to think about if & when to apply a protectant fungicide. We want to apply the fungicide long enough before a rain so that the residue dries onto the leaves and fruit. Then, rain can come after that, and the fungicide can protect from any rain that falls. Generally, a good protectant fungicide that is allowed to dry onto the foliage will protect for 7 days, no matter how much rain falls. Occasionally we get real deluges that test this theory. There are also “eradicant” fungicides that can be applied after a rain, and they can stop an infection even up to X hours after the rain started. In some cases X is as high as 48 hours!  Of course, these tools are usually more expensive than the protectant fungicides. It is nice to know that they are available, so if your sprayer breaks down at a critical time, an eradicant fungicide can serve as a safety net.

As of Monday April 17, 4% of the season’s supply of ascospores were ready for release in the Durham area.

Peach Leaf Curl

It is too late to control peach leaf curl this year. You’ll have to live with it.

Cedar-Apple Rust and Quince Rust

In the last issue, I showed a photo of the galls on a red cedar tree during the quiet winter. Once spring arrives, things start to change. During rainy weather, orange, fleshy telial horns project from the galls, and release the telial spores that infect apple foliage. One co-worker said the galls looked like bright orange Christmas ornaments. I thought that was a good description. The very first spore releases are around the time of tight cluster stage, and the major releases are at pink and bloom period. Quince Rust shows a similar pattern, though the galls (which are on common juniper) are difficult to spot. They are swellings in the juniper branches. To me, they are almost impossible to find, except when the fleshy orange telial horns are projecting. This photo shows them on a common juniper in Durham, on a rainy May 9th morning, 2013.

There are three ways to fight rust diseases on apples. One is to grow varieties that are not very susceptible to them. Another is to apply protectant fungicides during the period when spore releases are likely to occur. A third way is to remove all alternate hosts within 500 feet or so of your apples. With the exception of rusts that attack apple fruit, I don’t see enough injury to worry too much about them. The bright orange spots on apple leaves are easy to identify as rust lesions.

Mummyberry Fungus

Blueberries get attacked by fungi, too. The most serious disease I see is mummyberry, and the tiny fungal stipes should start growing from last year’s mummified berries (on the ground) soon. They begin as a dark brown stalk. Then the tip swells slightly, and a dimple appears at the tip, so it looks a bit like the head of a finishing nail. Then the tip expands still further into a tiny mushroom, and the color is light brown. These are the source of the spores that infect shoots this spring.

We manage mummyberry with several methods. One method is to bury last year’s mummies with at least 2 inches of mulch. That can be difficult to do if you have a large planting. You have to be sure you finish applying the mulch before green tissue appears (= before spores start getting released).

Another method is to apply a burning agent (urea) when the fungal stipes have started elongating, but before the fungal cups have opened. A third method is to apply protectant fungicides. For some growers with very small plantings, there is another option: Collect and deeply bury all fruit affected by this disease. The New England Small Fruit Management Guide has details on all of these options.

2017 Fruit-Related Events:

There are many events that might be of interest on our events calendar. Some events require registration or have fees, so you can see more details on our  events calendar.

Alan T. Eaton
Extension Specialist
Integrated Pest Management

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