A relatively new strawberry disease has made its way out of Florida and is spreading throughout the South and Northeast.
“Neopestalotiopsis is the name of the disease and the pathogen,” said Nicole Gauthier, Ph.D., Extension plant pathologist, University of Kentucky. “Most people call it Neopest. It appeared first in Florida during the 2017-18 winter growing season. It spread rapidly in the region, especially when the weather was warm and rainy. Plant and fruit losses were very high.”
Neopestalotiopsis is the genus, but the species is unknown.
“When a plant is stressed, Pestalotia will infect, often as a secondary pathogen,” said Gauthier. “Neopestalotiopsis is closely related to Pestalotia, except it isn’t opportunistic or secondary and it isn’t mild.”
Neopest doesn’t simply show up on a farm – it’s almost exclusively introduced by infected propagation material, most often plugs.
“Once it’s there, it spreads short distances by water/rain splash, workers, tools and other equipment – anything that carries debris and provides a way for spores to hitchhike around the farm,” said Gauthier.
The ideal environmental conditions for Neopest include prolonged leaf wetness resulting from consecutive rain events.
Gauthier said, “If you’re producing plugs, there are overhead mist systems giving [the pathogen] the water it needs.” Ideal temperatures for rapid sporulation and infection are between 60º and 78º F. However, sporulation can occur as low as 50º and as high as 86º.
Although Neopest is strawberry specific, closely related species may become infected and serve as a breeding bridge. Some weeds are affected but remain asymptomatic. The pathogen survives without a host in debris and soil. Colder temperatures help this pathogen survive.
“Survival is easily six months on the surface of the soil,” said Gauthier. “That’s when it’s dry and hot. If it’s buried, survival is 18 months or more. While fumigation does a good job, it isn’t 100% effective, and inoculum in row middles can splash its way back into the rows.”
She added that fumigation is expensive and not feasible for many small growers, and fumigating an entire field won’t completely destroy Neopest.
Symptoms appear on all parts of the plant, including crowns, roots, leaves and fruit. “It looks a lot like other diseases we know well,” said Gauthier. “That makes it even more difficult because by the time we identify it, it’s too late.”
Older leaves are the first to show leaf symptoms. The initial spots are circular, becoming irregular and blotchy before starting to coalesce and forming larger necrotic regions. The spots start out dark, then become light tan in the center with dark margins. Spots are scattered across leaves without a pattern. Lesions on the edges of leaves take on a V-shape.
John Rost prepares holes for strawberry plants for a Neopestalotiopsis disease resistance trial at the Southeast Agricultural Research & Extension Center in Lancaster County, PA. Photo by Sally Colby
“In the tan centers are acervuli, fruiting bodies, which are clusters of black spore masses,” said Gauthier. “That’s the tell-tale sign of Neopestalotiopsis.”
Leaf symptoms of Neopest look a lot like Phomopsis leaf spot, common leaf spot, strawberry leaf scorch and strawberry leaf blotch. The fruit rot also takes on the appearance of other diseases. Fruit lesions are light tan, irregular and sunken, and appear over the entire fruit. Acervuli develop in the center of lesions. Gauthier likens the appearance of lesions to anthracnose fruit rot.
When crowns become infected by Neopest or any other disease, there’s wilting as a result of girdling. Older leaves become reddened and new leaves are stunted. Orange-brown necrosis is visible in the crown. Crown rot and root rot symptoms appear most often during fruiting.
“Decay usually starts in the leaves and works its way to the crown, and it keeps going and works its way to the roots,” said Gauthier. “It’s a progression from upper to lower canopy. Infected roots become dark brown/black, and the plant dies.”
Management involves following the same pathogen rules recommended for every plant disease. Ideally, the pathogen is excluded. If it does come in, attempt to manage it.
“If you don’t have Neopest, don’t bring it in,” said Gauthier. “If there’s an area of your farm that doesn’t have it yet, keep it from spreading. Inspect plugs well in the fall, and when you move between fields, use caution. Work on the clean parts of the farm first, then the infested areas last.”
Wash equipment, clothing and boots after working in a contaminated area. Moving row covers can spread spores and contaminate storage areas.
Every mixed farm should be blocked or zoned. A standard practice is to rotate every three years. “When you block or zone, you know where there’s a history of disease,” Gauthier said. “Make your moves and rotations based on that.”
Remove infected plants so they cannot sporulate or drop infected debris on the ground. After the season, deep till to bury the debris so it decomposes more rapidly. Before the next growing season, deep till again.
“Always rotate with non-hosts for three or more years,” said Gauthier. “There are cases of Neopest overwintering for more than five years. If you have Neopest on your farm, use at least a three-year rotation, which is what we should be doing for lots of other diseases.”
It’s important to remember that fungicides don’t cure disease – they suppress disease activity. “They can bring the pathogen into a dormant state for two or three weeks,” said Gauthier, “then the pathogen becomes active again.”
For best results, apply fungicides after transplant and at 10- to 14-day intervals according to label directions. Consult Extension for assistance on appropriate products for your state and region. Fungicides are expensive, so it pays to do a risk/benefit analysis prior to application. If the crop is too far gone, it isn’t worth the investment in product and time.
Unfortunately, “resistant” varieties aren’t truly resistant – it just takes longer for disease to develop and spread. Gauthier said a resistance gene has been identified, but it will be used in breeding and it will be years before resistant plants are available.
“Any time a new disease starts, it’s the worst of the worst news,” said Gauthier. “It takes time for breeders and research to catch up. Hopefully a year from now we’ll be telling a different story.”
by Sally Colby
