Jul 2, 2012
Caring for trees in a no/low crop season

Trees that aren’t producing a harvestable crop this season still need care and maintenance.

Disease

Growers need to protect their trees against fire blight and be on the lookout for anything else that might damage the tree, said Amy Irish-Brown, a Michigan State University (MSU) Extension educator. Hailstorms are a major concern, as they can damage the cuticle of the tree and allow fire blight to enter the tree at the point of injury.

The loss of a crop may tempt growers to cut back on sprays, including Apogee, said Phil Schwallier, an MSU Extension educator.

“This will not be wise on fire blight-susceptible varieties, high-value orchards and blocks that had fire blight last year,” he said.

Additionally, applications of Apogee can help reduce excessive tree growth when crop load is light, according to Terence Robinson, a horticulturist with Cornell University. This can help in other areas of tree care.

Spraying around the terminal bud set is an important step in protecting the tree, but it might take longer this year, Irish-Brown said. In a normal season, it usually occurs in early July. Due to the lost crop, however, the tree will continue to produce vegetation and it will take longer for terminal buds to set.

Cherry leaf spot control is vital, said Nikki Rothwell, MSU Extension educator. The pathogen infects leaves, and even with no fruit trees are still susceptible.
Irish-Brown and other researchers have noticed more powdery mildew this year.

“I call it the 55 mph-drive-by disease, because you can see it so easily in the growing tips of the trees,” she said.

This could be a serious issue for growers next season, because it is so hard to control and can lead to serious overwinter injuries. Trying to knock it back when it is established is difficult, so the best thing to do is start controlling it before it really sets in, she said. Growers are expecting a lot of return bloom next year, and mildew outbreaks can jeopardize that.

Powdery mildew infection develops at 50˚ F to 77˚ F, and does not require moisture to germinate and multiply, said Noemi Halbrendt, a plant pathology research associate with Penn State Extension. Recent warm temperatures and vigorously growing shoots are perfect conditions for powdery mildew to explode. When powdery mildew takes off, it is difficult to manage once it gets established in the orchard.

The most important spray timing for powdery mildew control is the first cover timing, Rothwell said. The timing is a critical cost-saving measure. It will minimize the need to apply targeted fungicides later on.

Where the crop damage was extensive, growers may want to remove the few remaining fruits to avoid having to spray orchards for disease and insects, Robinson said. He cautioned that growers should check with their crop insurance agent first.

Bugged out

Growers will have to make their own calls when it comes to insect control, Irish-Brown said. They’ll still need to spray for foliar bugs, but the severity of the damage they cause can be limited by the health of the tree.

“Growers will find that the trees can tolerate leaf-eating pests more when there is no crop,” she said. “Trees can handle quite a bit more defoliation and still be healthy when they are not spending energy producing fruit.”

Oblique-banded leafrollers overwinter as larvae; as leaves develop, they move to the terminals to feed, Rothwell said. In a block with no fruit, a money-saving strategy would be to spray either the spring overwintering larvae or the summer-generation larvae, rather than spraying at both times. The cool spring is pushing growers to plan to spray for the summer generation.

Growers who intend to harvest a limited crop may need to ramp up protective sprays for insect damage, Irish-Brown said.

“Even though a grower may only have a 10 percent crop, there is still going to be 100 percent of the pest, like codling moth,” she said. “We’ve already seen that this year with plum curculio. A block had a few apples left, and every one we examined had plum curculio scarring.”

Cutting back on spraying can have repercussions for the following year.

“Trees with minimal fruit are more likely to be infested, as there are simply fewer fruit in which plum curculio or cherry fruit fly females can lay eggs,” Rothwell said. “Insecticide sprays for plum curculio and cherry fruit flies can be eliminated, but growers should keep in mind that eliminating insecticide sprays could result in higher insect populations the following season.”

Planning for next year

For many cultivars, this season’s crop loss will result in intense flowering next year, especially in cultivars with high vigor, Robinson said.

Controlling vigor is vital to the health of your trees. Reducing or eliminating the application of nitrogen is one way to control vigor, Robinson said.

“Growers who have either not applied nitrogen yet or have split their nitrogen application in two parts can reduce or eliminate further nitrogen this year,” he said.

Another way to control vigor is with root pruning at bloom to 10 days after petal fall, Robinson said. It can be very effective in controlling excessive shoot growth. There are two types of root pruners, the knife-shank type or the coulter-wheel.

“We recommend the use of a coulter wheel over the knife-shank, since it doesn’t cut as deep and minimizes the damage to larger and deeper structural roots of more mature or older apple trees,” he said.

Another thing growers need to be aware of is drought, Irish-Brown said.

“Growers really need to be aware of water need, and irrigate as needed. Protect those young trees especially,” she said.

In peaches, it is most important that growers make, at minimum, big pruning cuts, allowing ample light to reach the lower branches so that they will not die out, said Paul Friday, a peach breeder from Coloma, Mich.

“After the winter freeze of 1999, growers who did not prune their peach orchards lost a lot of their lower bearing surface,” he said. “The natural tendency of a peach tree is to grow upwards. Keeping the cropping surface low for pedestrian harvesting requires vigilant attention. A crop-less tree is going to put on more new growth and shading than one with a crop. Thus, more attention to this matter is needed this year, rather than less.”

By Derrek Sigler, Assistant Editor





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