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Fruit trees at Cherry Hill Orchards in Lancaster, Pa. Chris Torres
WAIT AND SEE: Trees are past bloom at Cherry Hill Orchards in Lancaster, Pa. Recent cold spells have likely damaged fruit flowers in many areas, so experts are warning against widespread thinning.

Hold off on thinning fruit trees after recent cold weather

Recent cold bouts have come at the wrong time for apples, peaches and other tree fruits.

There was a touch of summer in the air on Friday, which likely allowed many growers in the region to get caught up on planting.

But the recent cold hasn’t been kind to fruit growers. Another cold snap earlier this month put blooming apples and peach trees under more stress.

Barron Shaw, owner of Shaw Orchards in White Hall, Md., says he’s desperate to see good growing weather.

“We lost a good bit of our peach crop around April 17,” he says. “It got down to about 29 [degrees F] then. This most recent freeze killed some more of the strawberries that made it through the first cold spell. It also froze some of our late-blooming apples that are almost always safe this time of year.

“I don't think we lost all of anything, which is pretty remarkable given how bad the weather has been. The plants are definitely desperate for some good growing weather because they came out of dormancy so long ago. Strawberries, which at first were on track to be weeks early, now will be weeks late.”

Daniel Weber, tree fruit Extension educator for Penn State Extension Adams County, says it’s largely a wait-and-see game to determine what the effects of the cold will be on fruit production.

Cynthia Haskins, president of the New York Apple Association, says there has been minimal damage reported in most of New York’s apple growing areas, though pockets of the Hudson Valley have seen more damage.

“We’ll just have to watch the weather over the next few days,” she says. “I think New York may have escaped getting anything.”

Assessing cold damage

The mid-April cold spell involved a temperature inversion where trees in lower elevation saw lower temperatures than trees on slopes or on higher elevation. As a result, some growers likely saw widespread damage in low-lying areas but little to no damage on slopes.

The most recent cold snap was much more uniform and, given the fact that most trees are either blooming or past bloom, they are much more sensitive to cold snaps. Prolonged temperatures below 28 degrees for three to four hours, he says, can cause lots of damage to blooming trees.

Go online to find a Michigan State University chart that explains critical temperatures for tree bud development.

Most areas of Adams County didn’t get below 28 degrees for long periods of time, he says, but neighboring counties did, including areas of Blair County, where temperatures hovered between 19 degrees to 21 degrees.

Given the fact that trees have likely experienced some sort of damage, Weber and others recommend against scheduled chemical thinning, telling growers to wait and see how the crop develops.

“Pay attention to fruit that does set and be super cognizant to the fact that you don’t want to over-thin,” he says.

In a posting on the Penn State Extension website, Jim Schupp, professor of pomology at the Fruit Research and Extension Center, says fruits that are destined to die may remain on the tree until 7 or 8 millimeters in diameter.

“If you see evidence of flower damage it is suggested that you wait until the fruits have grown to 10-12 mm in diameter before deciding if you need to thin this year,” Shupp writes. “The April freeze may have done some or all your thinning for you and this may not be evident until the surviving fruits have had an opportunity to grow.”

Weber says growers should be doing bud surveys and taking random samples at multiple elevations to check for damage. He says to take at least 100 samples from a given location, look at the ovaries of the flowers and check to see if they have turned brown. If they have, they are likely dead and will need to be recorded for crop insurance purposes.

Playing catch-up

Most growers have a lot of catching up to do when it comes to field crops. The May 10 Crop Progress Report shows only 5% of corn in Pennsylvania planted, well-below last year’s pace of 23% and the five-year average of 32%.

Oats are 60% planted, below last year’s pace of 81% and the five-year average of 82%.

Only 21% of corn in Maryland is in the ground, well-below last year’s pace of 58% and the five-year average of 50%. Winter wheat is ahead of schedule, though, with 87% of the plant heading, ahead of last year’s pace of 67% and the five-year average of 46%.

In Delaware, 24% of the state’s corn has been planted, behind last year’s pace of 43% and the five-year average of 53%. Winter wheat is slightly ahead of schedule with 57% of the crop heading, slightly ahead of the five-year average of 48%.

New York growers have started planting corn, a big change from last year when many growers either had to wait until the end of May or early June or claimed prevented plant acres as a result of cold and wet conditions. Corn is 8% planted, behind the five-year pace of 13%.

Oats are 36% planted, ahead of last year’s pace of 26% but behind the five-year average of 46%.

Barley is 29% planted, behind the five-year average of 34%.

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