Fruit Bud Stages Now
At the Woodman Horticulture farm in Durham, fruit buds on Monday April 21 were:
Pioneer McIntosh Apple: advanced green tip. Japanese plums: bud burst. Peach: swollen buds. Blueberry: swollen buds, some varieties with loose bud scales.
Overwintering and Spring Pest Activity
Especially for insects, the overwintering stage affects how quickly a pest can begin attacking your crop. If it is in the adult stage, it may be ready to feed, or lay eggs right away. If it overwinters in a different stage, then it usually takes longer to become an active threat. Tarnished plant bugs and pear psyllas overwinter as adults, and are ready to attack your fruit trees as soon as the weather warms in the spring. Typhlodromus pyri (predator mites) overwinter under scales of bark near the base of fruit tree trunks. They begin activity after the buds have opened and weather warms. I expect their numbers to be low this year, from the long, cold winter.
Apple grain aphids (AGA), European red mites (ERM), and Eastern tent caterpillars overwinter as eggs. AGA hatch and start feeding on the opening apple buds right away, but are not a problem. ERM eggs usually hatch during the pink stage of apples. For years, tent caterpillar eggs hatched on or about April 15th in southern NH, but in recent years that has shifted earlier. We’ll see if it is back to April 15th this year. Plum curculios are still in leaf litter in the woods. It will be late May or June before they become active. Codling moths overwinter in cocoons the caterpillars constructed last fall. They are usually on the trunk, well camouflaged in bark crevices. The caterpillars that survive the winter transform into pupae in the spring. The adults emerge in June. Green pug caterpillars are a problem for some growers during bloom. They overwinter as eggs that were laid on the buds last year. The eggs usually hatch in April, when new apple foliage emerges from the buds. I do not know how sensitive they are too cold winter temperatures. Since they are exposed, maybe fewer of them will survive than usual this year. Tentiform leafminers are in the pupal stage, in mines in dead apple leaves on the ground. The adults emerge starting at about ½ inch green stage.
Fungi: Understanding how & when the fungal pathogens overwinter helps us understand where sanitation might help, and when attack might begin. Apple scab fungus overwinters in last year’s dead leaves. Over the fall and winter, inside the leaves, the fungus produced perithecia which are now filled with sacs containing the ascospores. As spring advances, the ascospores mature. When daytime rains fall, the mature spores get released. In New England, North American brown rot fungus overwinters in cankers. The fungus produces conidia in spring, which are splash spread. The European brown rot fungus (Monilinia laxa) overwinters the same way here. Farther south, North American brown rot fungus also overwinters in mummified fruit. The fungus can produce apothecia from mummies on the ground, if conditions are right. Mummyberry fungus overwinters in last year’s mummified blueberries, on the ground. When the blueberry buds open and green tissue is available to attack, the fungus grows a stipe out of the old berry. It opens into a cup, and releases ascospores during rainy weather
Apple Scab
The snow finally melted from around my apple trees on April 9, but water was still pooling at the surface, suggesting the ground beneath was still frozen. If your orchard has firm soil, it may not be too late to try leaf shredding to help reduce the amount of overwintering inoculum. In part, disturbing the leaves works because many get turned upside down from the position in which they laid all winter. The perithecia form with the openings pointed up. If you come and turn that leaf over, the spores (when released by daytime rains) will shoot down. I don’t expect the very first spores to be mature until some green tissue appears on the apples. The fungus is pretty well coordinated with the trees’ growth, with the exception of a really dry period that can interrupt spore maturation/development. For those who monitor degree days to predict ascospore development, the biofix (time when temperature measurements begin) is when 50% of McIntosh fruit buds are at green tip stage.
Peach Leaf Curl
For growers who had problems with peach leaf curl last year, a fungicide application either last fall or now could help. If you missed the fall window, you might have an opportunity to apply a fungicide , if the buds have not yet started swelling. Bravo, C-O-C-S, Echo, Ferbam, Kodide, Thiram and Ziram are all options. The New England Tree Fruit Mgmt Guide has details. Peach leaf curl can be especially bad if you had no fruit last year. The fungus can build up when we do not apply brown rot fungicides.
Symptoms of the disease are thick, curled, reddish, distorted new foliage. Once the foliage is out, we have no effective treatments.
New Rules on Currants in NH
We were disappointed to learn that the fungus that causes white pine blister rust (and has Ribes as one of its two hosts) has overcome the resistance in the currant varieties now legal for growing in New Hampshire. This and results of examining plantings for evidence of the fungus has triggered changes in the list of species/varieties allowed for planting in NH. Click here to see the new list.
It could be that other changes are coming, but that is what I learned so far.
Leafminer Traps
Traps to monitor apple blotch leafminers and spotted tentiform leafminers are large, dark red sticky rectangles. They work well to predict whether or not you have enough LM’s to require treatment. I find that populations vary a LOT from orchard to orchard. You can buy the traps from Great Lakes IPM. I use long push pins to attach them to the south or southeast side of the apple trunk, at knee height. I put a pin through each corner, and occasionally I put another in the top center margin as well. This usually keeps wind from blowing them off. In this photo, the grower used a staple gun. When do you hang them? Place them at the ¼ inch green stage. I concentrate the few I place, in spots where I remember LM numbers were high last year.
Mummyberry
There are several management techniques for mummyberry that are appropriate in spring. Applying a 3 inch layer of mulch is designed to bury last year’s mummified fruit deeply enough that the fungal stipes cannot emerge and release spores. That should be done before any green tissue shows on the swelling buds. If you missed that deadline, and had a lot of mummyberry last year, you might want to try the urea treatment. It is designed to burn back the emerging fungal stipes before they open up into a cup. The New England Small Fruit Management Guide has more details, but one key point is not to apply urea to wet spots in the field. That can cause phytotoxicity to the plants. My two April 2011 photos show the fungal spike (stipes) emerged and just starting to form a cup in the first photo, and an opened cup in the second photo. These are the source of the ascospores that infect the blueberry shoots.
Alan T. Eaton, Extension Specialist, Integrated Pest Management
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Mummyberry
There are several management techniques for mummyberry that are appropriate in spring. Applying a 3 inch layer of mulch is designed to bury last year’s mummified fruit deeply enough that the fungal stipes cannot emerge and release spores. That should be done before any green tissue shows on the swelling buds. If you missed that deadline, and had a lot of mummyberry last year, you might want to try the urea treatment. It is designed to burn back the emerging fungal stipes before they open up into a cup. The New England Small Fruit Management Guide has more details, but one key point is not to apply urea to wet spots in the field. That can cause phytotoxicity to the plants. My two April 2011 photos show the fungal spike (stipes) emerged and just starting to form a cup in the first photo, and an opened cup in the second photo. These are the source of the ascospores that infect the blueberry shoots.
New Hampshire Integrated Pest Management Newsletter 