Prunes Continued from Page 9
more risk of rain-splashed spores be- cause of the additional time it takes to hand-prune. Because mechanical hedging and topping are much faster than hand pruning, the brush can be removed im- mediately and allow for an application of Topsin M, a protective fungicide that he said helps prevent the infection of spores during rain. Cytospora is really spread by water splash, and spreading the spores is the main concern, Milliron stressed. Cytospora is also on the orchard floor, and there’s concern that these micro- droplets could splash up into the lower canopy. Because of this, he recommends removing and burning the brush if possi- ble, to prevent any spread. Milliron also advised sterilizing hedg- ing and topping equipment between or- chard blocks, especially because there are several fungal cankers to which prunes are susceptible. With low prices for prunes, labor costs continually increasing and limited em- ployee availability, Milliron said many large growers in his area are looking at mechanical hedging and topping instead of hand pruning. Milliron said he is involved in a study looking at the effect of mechanical hedging and topping. The research has been going on about two years with dif- ferent hedging and topping times and treatments. There is also a hand prun- ing treatment. So far, he said, there hasn’t been any Cytospora in the research blocks, but it is a young block, and he said it’s ex- pected they will see the disease in the next few years. (Kathy Coatne y i s a repor t e r in Bend, Oregon. She may be contacted at kacoatney@gmail.com.)
young interplants, and you know there’s Cytospora present,” he said. “There’s Cytospora in nearly every mature orchard, so the chance that that tree will get infected from Cytospora and not live tomaturity is high,”Milliron said, which is why he suggests farmers consider replanting the entire orchard instead of interplanting. Most wounds come from pruning— topping, hedging—or harvesting. “It could be coming in certainly from sunburn, oil burn, and from potassium deficiency, too,” Milliron said. Prunes are a potassium-hungry crop, so a potassiumdeficiency is something to watch for, he said. Preventing prune trees frombecoming potassium-deficient is in the same category as water deficiency, he added. “Water deficiency inprunes is definite- ly tied to potentially more Cytospora,” Milliron said. “If you have severe potas- siumor water deficiency, Cytospora that is already present will just spread like wildfire. The cankers will literally move faster in their growth.” Shaker thinning in the spring is anoth- er potential source, he said, but it hasn’t been studied yet. “Whether those tiny, little abrasions and the removal of the fruit, if followed soon after by rainfall, is an important
Prune cankers have been removed from this branch. Prune trees can be susceptible to both fungal and bacterial cankers.
entry for Cytospora, is unresearched,” Milliron said, “but pruning wounds are probably the No. 1 injury.” There are pros and cons to mechan- ical hedging and topping versus hand
pruning, he said. “With hedging and topping, making these mechanical cuts, you’re just mak- ing zillions of cuts across the orchard, so youhave zillions of entry points,”Milliron said. “At the same time, thosewounds are often relatively small, so they heal faster than a large cut would.” Abig advantage tomechanical hedging and pruning compared to hand pruning, he said, is the ability tomove through the orchard faster. “It’s harder to protect the wounds if you’re hand pruning, because you’re moving across the blockwithhand crews over time,” Milliron said, adding there is
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10 Ag Alert January 27, 2021
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