Feb 4, 2019

New options available for battling orchard nematodes

Nematodes are a threat to the productivity of both new and established orchards, but new products and research are adding to growers’ collective toolbox for dealing with the pests.

Marisol Quintanilla, an applied nematologist at Michigan State University (MSU), is taking part in a study about the problem of replanting orchards, for which the tiny worms are an important player.

But even once the orchards are established, nematodes such as root lesion and root knot reduce yield and vigor, she said.

Other nematodes are gateways to other pathogens.

“For example, dagger nematodes can vector viruses such as tomato ringspot virus, tobacco ringspot virus, peach rosette mosaic virus,” she said. “Tomato ringspot virus affects cherries, peaches, apples, grapes, raspberries, blueberries and strawberries. On each, it produces different symptoms and weeds such as dandelion are also host for the virus and can be an important infection source.”

Diagnosis

Growers often diagnose nematode problems based on a lack of vigor in the orchard.

“Growers who have fields infected with high levels of nematodes will see an overall reduction of vigor and yield, they will see a lack of spur growth, which is needed to produce heavy yields, and a lack of overall health,” said Ryan Garcia, a pest control advisor and certified crop advisor for Salida Ag Chem located near Modesto, California. “If ring nematodes are present then growers, especially in sandy soil areas, may also see signs of bacterial canker and bacterial blast.”

Quintanilla said viruses spread by nematodes also have particular symptoms.

“For example, in peaches and cherries, tomato ringspot virus causes stem pitting, might have thickened spongy bark and pits in the wood underneath, close to the soil line,” she said. “There are also symptoms in the leaves, such as delayed unfolding of leaf buds. Leaves might also turn color prematurely. In apples, it causes brown ring necrosis.”

Professional help is often necessary for pinpointing the exact nature of the problem, and depending on the region, both public and private labs may be able to assist. Some universities such as MSU operate plant diagnostic labs that analyze soil samples from growers. Bayer Crop Science also offers a Soil Nematode Analysis Program, or SNAP, a service for commercial growers.

Products for control

“There are several new nematicides in development or newly developed,” Quintanilla said. “Not all are available for fruit trees.”

In the past, fumigation and nematicides such as Vydate have often been used, she said.

“There are also new products that are safer, but not all have the same effectiveness,”Quintanilla said. “We have not yet tested these products in fruit trees, but have tested several in other crops.”

Garcia often recommends products from Bayer to help knock down nematodes when pressure rebuilds in established orchards.

“Velum One is a soil-applied material that also helps suppress nematodes in the soil and therefore promotes the growth of healthy roots while maintaining the health and vigor of the current root system,” he said. “Velum One suppresses a wide spectrum of nematode species, including all of the species we deal with in tree crops, and it also has some fungicidal properties in various crops. This soil-applied product provides a different option for the grower to include in their nematode management program and its ease of use along with proven results make it an appealing option.”

Velum One was first introduced in 2017. It is registered in California and Arizona for a variety of tree fruit crops including cherries, pome fruit, peaches and tree nuts, according to the Bayer website.

Quintanilla said Velum was a part of trials at MSU, and has shown efficacy in reducing nematode numbers or increasing plant growth.

“It does not eliminate nematodes, so it will not eliminate the problem, but decrease it,” she said. “It can be used as an additional tool to manage these problems. We have not tested this product on fruit trees, but we are basing our answers on results in other crops.

In order to be effective, it needs to be applied directly to the plant roots, foliar applications will not result in nematode control.”

Another Bayer product, Movento, is registered in all states. Unlike Velum, it is applied to the tree leaves.

“Movento is a good product for protection against nematodes and other pests,” Garcia said. “It is foliar applied and moves systemically throughout the tree and is able to move down into the roots where it’s needed for nematodes suppression.

Movento has a unique mode of action and is able to suppress all of the major nematodes that we deal with in tree crops.”

Other options

Thoughtful growers can take many steps to prevent nematode problems in established orchards.

“I would say that an important step in reducing the nematode population is pre-plant practices, specifically removing any old root material and fumigating the soil prior to planting,” Garcia said.

He said nutrition programs and water management are also important to promote root growth and thus recovery from nematode damage. “Growers need to know their fields and know the issue that can arise in order to plan ahead,” he said.

MSU researchers have also experimented with non-chemical techniques.

“In our trials, we have found that some composted manures such as the Layer Ash Blend from Morgan Composting reduce nematode numbers,” Quintanilla said. “There are some cover crops that reduce certain nematodes, but it is recommended to do a soil test before choosing a cover crop.”

The challenge in choosing the right cover crop, she said, is that there are several types of nematodes and each can be reduced by different cover crops.

“It is also important to know that different varieties of the same species of cover crops might have different host status and might impact nematodes differently,” she said.

– FGN Associate Editor Stephen Kloosterman

Above: Ryan Garcia is a pest control advisor and certified crop advisor for Salida Ag Chem located near Modesto, California Photo: Bayer