Fruit Bud Stages
In the Durham area, McIntosh and Cortland apple fruit buds were at late pink stage on Monday morning May 8th. A couple of king blossoms were threatening to open. Peaches still had petals… about 70% of the petals had dropped. Blueberries were at pink bud stage. Raspberries have some new primocanes emerging from the ground up to 4 inches high, and the very first flower buds were visible on the bearing canes.
The largest ascospore releases during primary apple scab season usually occur around the time of pink or bloom. The rate of spore maturation is high then, and we have lots of exposed tissue available for infection. As of Monday May 8, the apple scab model forecasted 66% of the season’s spores were ready for release and 55% had already been released. Meanwhile, any spores that had started new infections this year have grown into lesions that soon will be producing conidia, which are infective spores that get spread by splashing. Conidia can be spread at night, but ascospores only get released by rains that fall during the daytime. You knew that, right?
Monitoring Leafminers in Apple Orchards
Not every apple grower sets out red sticky rectangle traps to monitor leafminer adults. For those who did not use the sticky traps, there is another way to monitor leafminer populations. It involves looking at the undersides of leaves, for the sap-feeding mines. You have to wait until about a week or so after petal fall for the mines to show up. They remain in this stage for perhaps a week to 10 days. So I’m showing this photo now, since I might not have a newsletter issue that comes out right at that time. Turn the leaf over and look at the undersides. Sap feeding mines show up as slightly silvery areas. Basically, the miners have severed the lower epidermis from the spongy palisade layer of the leaf. If you see 13 or more mines out of 100 CLUSTER leaves, it is worthwhile to apply an insecticide to control them. Once the miners get bigger, they begin feeding on the spongy layer in little clusters. That creates spots that soon become visible on the upper side of the leaf. That signals the end of the period when the caterpillars are vulnerable to insecticides. By the way, in this photo I see 4 sap-feeding mines on the same side of the mid-vein as my thumb. In real life, tilt the leaf a bit, if you are unsure. Another trick is to use a pin or knife tip to try & peel away the epidermis. The tint, translucent caterpillar should be there somewhere.
Tent Caterpillars and Gypsy Moths
Both of these are common backyard tree fruit pests that are easily controlled if you act early. The larger the caterpillars get, the more damage they have already done, and the harder they are to control. There are actually two species of tent caterpillars, forest tent caterpillar and Eastern tent caterpillar. Both are easily controlled with Bacillus thuringiensis-based insecticides, but could use synthetic chemicals too. Not only are they easier to control when small, they have also done less damage then.
Gypsy moth is usually held in check by an insect-killing fungus. But the southeastern part of our state has experienced drought the last two growing seasons, so gypsy moths are building up there. Gypsy moths are tougher to kill with B.t.- based insecticides, but they work if the caterpillars are small… perhaps shorter than 1 inch. By the way… B.t.-based materials must be sprayed on the leaves the caterpillars eat. They do not work by contact action. Most chemical insecticides work both ways… both as stomach poisons and as contact poisons.
Insect Pest Activities in Apples During Bloom
Adults of codling moth begin laying eggs about the time of full bloom to petal fall. That’s also the same time that males of San Jose scale do their flying. Since a couple people are trying pheromone traps to monitor SJS this year, I include this old drawing of a male from a USDA bulletin over 70 years ago. They are only 1 millimeter (1/25 inch) long. For those of you monitoring SJS with these traps, the number of males you find is not very important. It is WHEN they appear, so I’d check my traps every day or two. That starts the clock ticking to predict crawler emergence by calculating degree days. What else is happening then? Eggs of European apple sawfly are beginning to hatch. Lesser appleworms should start flying. Plum curculios should start moving into orchards, if the weather is favorable. They won’t begin attacking the fruit until the first fruit reach ¼ inch size. Then, they attack heavily, usually for about 3 weeks. They can totally eliminate your crop.
Mummyberry Disease of Blueberry
The fungal cups that I showed in the last newsletter produce ascospores that are released in rainy weather and infect young blueberry leaves. Now it is time to show the next part of the cycle. Those primary lesions (photo below) produce fungal spores that are splash spread and infect the green fruit. At first, there is no outward sign that the fruit are infected. But eventually they start turning a salmon color, and then start becoming ridged, like a pumpkin, and drop to the ground. The fruit stay on the ground all season, becoming black, dry and ridged. Then the following spring, fungi grow from them and the cycle repeats.
Blueberry Pollinators and “Cheaters”
Since the large carpenter bee reached New Hampshire a few years ago, we have seen more blueberry corollas with holes in the base. What’s going on? Large carpenter bee has strong jaws, and often chews a shortcut to reach the nectar. That means that it doesn’t really contribute much to pollination, when it does this to reach nectar. Other bees don’t seem to do this. What can you do about it? Probably nothing, so don’t worry. Carpenter bee looks just like several species of large bumble bees (which are good blueberry pollinators by the way) except that it has a SHINY black abdomen.
This tiny (2mm long) weevil is also known as strawberry bud weevil. It overwinters as an adult, and usually appears in May, just as the first fruit buds of its major host plants (strawberries, raspberries and blackberries) are appearing. The female beetles attack the unopened flower buds by laying an egg inside. Then they sever the petiole, and that bud will never produce fruit. Damage is typically worst at the edges of a bed, especially if woodland is on that side. Sometimes we can see a significant amount of injury, and in other spots or other years, there is very little. If you look at the New England Small Fruit Management Guide, you’ll see a sampling procedure and thresholds to help you determine if it is worthwhile to treat a bed for this insect. It is worthwhile to do the monitoring, rather than guessing if there will be a problem… or just automatically treating.
Organic Weed Control in Lowbush Blueberries
My colleague Olivia Saunders finished a SARE grant on this subject, and recently placed a report you could read, if you’re interested. Bill Lord assisted setting up this project, which especially focused on poverty grass. Here is a link to that report https://extension.unh.edu/resources/files/Resource006566_Rep9432.pdf
We thought that lowbush people might like to learn more, so Olivia has set up a meeting at a lowbush site in Milton, on May 31st. See the UNH Cooperative Extension events calendar for more details.
Do you ever find a small, tan, segmented “worm” in the raspberries you picked? Those are most likely raspberry fruitworms. Usually they are not a significant problem, but in some plantings there are a lot of them… enough to discourage customers. The problems from this insect begin early, and the adults are tiny (3mm) oval, tan beetles. They are active on opening raspberry and blackberry vegetation, and sometimes they chew up the opening fruit buds. If you see what you think are a significant number of them, you might consider applying an insecticide before bloom to kill them. After bloom, the females lay eggs inside the green fruit. The eggs hatch into the segmented tan larvae, which feed on the receptacle. When the ripe berry is picked, the larva often ends up inside.
Alan T. Eaton
Integrated Pest Management
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