Orchardists face tricky decisions on crop load and pest management thanks to a late spring wave of cool weather.
“It’s very difficult in a year like this to have a straightforward plan,” said Greg Krawczyk, a Penn State Extension entomologist.
He spoke at a Penn State twilight meeting April 25 at Cherry Hill Orchards.
Unusually warm early spring weather got bloom going earlier than normal, but the return to more seasonable temperatures has slowed the trees’ progress.
In Lancaster County, the temperatures have not been cold enough to produce more than spotty frosts, too close to the ground to injure apple crops.
“Fingers crossed. We’ve got a few more weeks yet,” said Tim Elkner, an Extension educator in Lancaster County.
But the temperatures forecast for the next week are low enough — highs in the 50s and 60s — to reduce the effectiveness of chemical thinners.
That’s problematic because, in Adams County at least, good bloom and pollination periods have led to a strong initial fruit set.
“That’s a happy dilemma. That means that we’ve got a crop to work with, but we’re going to have to get to work,” said Jim Schupp, a Penn State tree fruit researcher.
Chemical thinners are thought to work by inducing carbohydrate stress, causing the tree to shed fruit. But at the expected cool temperatures, trees will not be consuming carbohydrates quickly.
“It’s hard to induce a carbohydrate stress on a tree that’s only sipping from the cup,” Schupp said.
Chemical thinning works when fruits are 7 to 17 mm and performs best at 10 to 12 mm. Many fruits were 5 or 6 mm early this week.
Fruits can grow 1 mm a day in warm weather, so in an average year, farmers would be in a seven- to 10-day window for applying their thinners.
The cold will slow fruit growth, so the opportunity may last a little longer than normal. But even so, growers may want to hold out until fruits are 15 to 17 mm, looking for temperatures at least in the 70s.
“You might be waiting to the ragged, jagged end,” Schupp said.
If growers feel they must thin in cold weather, carbaryl and NAA will be the most effective options. 6-BA is ineffective below 70 degrees, Schupp said.
Once the ideal thinning window has passed, growers who still have too many fruits may want to make a rescue thinning treatment. Accede or the more powerful ethephon will be the best options, Schupp said.
This spring’s warm-then-cool weather has also complicated insect management.
The imminent petal fall spray should target oriental fruit moth, plum curculio and European apple sawfly. Growers who have had past problems with the curculio or sawfly should spray as soon as it makes sense, Krawczyk said.
Source: lancasterfarming.com
Photo Credit: gettyimages-richard-7
Categories: Pennsylvania, Crops, Fruits and Vegetables, Weather