Mar 22, 2017
Cranberry school covers fruit rot, other threats

If Wisconsin cranberry growers had a higher incidence of fruit rot in 2016 than usual, should they intensify their fungicide spray program this coming season? Not necessarily, said University of Wisconsin (UW) Extension plant pathologist Patty McManus.

Speaking at the 2017 Wisconsin Cranberry School, McManus said that the level of fruit rot in one growing season is generally not a good predictor of levels growers might see of the fungal disease the following year on Wisconsin cranberry marshes.

While fruit rot is a significant problem for cranberry growers in Massachusetts and New Jersey, the disease occurs more sporadically in Wisconsin, McManus said.

“So if your fungicide program worked well in 2016, then don’t change a thing, as clearly you are doing something right and you should probably be giving this talk next year,” McManus said.

In cases where a fungicide program did not work well, McManus advised growers to review their choice of fungicide, product efficacy, application rates, coverage and timing. For example, storing the product where it can freeze or get damp could reduce its effectiveness, she said.

McManus also said growers should determine whether the fruit rot they observed was caused by pathogenic fungi, or if sunscald or other environmental stresses caused the rot observed in cranberries.

In a three-year study conducted by McManus and Lindsay Wells-Hansen, the pair looked at the levels of fruit rot in test plots that received no fungicide applications at three locations.

Test plots at the New Jersey cranberry research center showed the level of fruit rot increased each season with no fungicide applications. The amount of fruit rot in plots on two Wisconsin cranberry marshes, however, remained the same or decreased.

In his 2016 fungicide trials, UW-Madison horticulture researcher Jack Perry observed 30 percent to 60 percent fruit rot in his untreated check plots.

“2016 was a pretty intense year for diseases for a lot of folks. Not sure exactly what the reason is for that, but I still think that April and May have a lot to do with determining how intense the disease pressure is going to be for that particular season. I also think the history of that bed has something to do with it, too,” Perry said.

In Perry’s 2016 trials, plots receiving two applications – the first at 10 percent bloom and the second application 10 to 12 days later – had less fruit rot than plots receiving a single application at 50 percent bloom.

“Whatever you miss with one application, you can pick up with the second one. It gives you some wiggle room. Save money somewhere else, but don’t do it by skimping on your fungicide applications,” he said.

Among the new fungicides Perry tested in his 2016 trials was Quilt Xcel, a combination of Abound and Orbit, which performed well. Used at the full rate, the product costs $30 per acre.

“I tested it at the 22-ounce rate, but I think that’s a bit of overkill. I think we can get by with less and still get a good level of control,” he said.

Perry also tested Kenja, a new bio- type fungicide, which was recently registered for use on cranberries. Although not impressed with the first-year results in his study, Perry will be taking another look at the product this season.

Discussing several “escape weeds” that are difficult to control on cranberry marshes, Perry said he has still not found any herbicides that can be sprayed over the top of cranberry vines to control seedling maple trees.

But Weedar 64 (a liquid 2,4-D product) is once again labeled for use on cranberries as a wipe application. Perry said the best time to wipe the maples is early in the growing season before the leaves develop a waxy layer.

Moss drift

Another problem weed for cranberry growers is moss, said Jed Colquhoun, UW Extension fruit and vegetable production specialist.

Colquhoun said there is an experimental product that is showing some promise on controlling moss in cranberries. The manufacturer will be working toward getting the product approved through the federal minor crops pesticide registration program this year, he said.

“And that’s great, but what I can tell you is that it’s a short-term solution. Until you get good drainage, moss will keep coming back. It sporulates and reproduces prolifically once it gets a foothold. Drainage is really the only long-term solution,” Colquhoun said.

A project Colquhoun hopes to work on would look at which weed species affect cranberry production. Compared to other fruit and vegetable crops, there is little data on the economic impact specific weeds have on cranberry yields and fruit quality.

“I agree that there’s nothing better than driving by a bed and seeing not a weed in there. But in an economy like this, is it something we need to spend a lot of time and money to go after, or is it more of just an aesthetic concern. We just don’t have good data,” he said.

Colquhoun also discussed the introduction of varieties of soybeans, corn and cotton resistant to 2,4-D and dicamba. About 1 million acres of dicamba-resistant soybeans were planted in 2016, and it is estimated 15 million acres will be planted this spring.

“In Wisconsin it’s a concern because specialty crops are widely dispersed throughout the state. Our broadleaf specialty crops, in particular, do not like 2,4-D or dicamba exposure. So herbicide drift is a very high risk,” he said.

Although EPA had not approved the use of dicamba for applications on growing soybean or cotton plants in 2016, complaints of alleged misuse of the herbicide were received from Alabama, Arkansas, Illinois, Kentucky, Missouri, Minnesota, Mississippi, North Carolina, Tennessee and Texas.

The Missouri Department of Agriculture reported that through August 2016, it had received 117 complaints alleging the misuse of pesticides containing dicamba. Growers reported that off-target movement of dicamba had adversely affected more than 42,000 acres. Crop damage was observed on peaches, tomatoes, cantaloupes, watermelon, rice, cotton, peas, peanuts, alfalfa and soybeans.

Colquhoun encourages cranberry growers to be aware if nearby farms are planting dicamba- or 2,4-D-resistant corn and soybeans, and to have discussions with their neighbors about non-target movement of dicamba, 2,4-D and other herbicides.

— Lorry Erickson, FGN correspondent

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