Disease pathogens and soil-inhabiting insects in cereals

Unfortunately, it’s not just soilborne pathogens that can harmfully impact root health – certain soil-infesting insects can cause gradual yet severe damage and economic loss, too. Wireworms are among the most difficult insects to detect, and as with soilborne pathogens, symptoms are tough to observe until bare patches and thin stands appear in fields.

Differing greatly in habitat, size, feeding patterns and susceptibility to insecticides, wireworms are small pests that typically feed on plant crowns, developing roots, germinating seeds, and specifically, wheat kernels’ endosperms, leaving behind only the seed coat. As they move upward in the soil, they can even attack wheat as soon as the crop is seeded. Populations of this pest can be found as high as 1.2 million wireworms per acre, and depending on the species, they can concentrate in low, poorly drained fields or in high, drier areas. Typically, wireworm damage is most severe where wheat was seeded after fallow or after a number of years of grass growth.

Bob Vernon, Ph.D., with the Canada-based Pacific Agri-Food Research Centre, is a global leader in wireworm research who has been conducting wireworm surveys since 2004.

“Wireworms are attracted by carbon dioxide," Vernon explained. “So as wheat germinates, wireworms will cue in on that carbon dioxide trail and move in to feed. What we’ve found in the lab is that large wireworms can easily consume two or more seeds, and they also eat roots and other growing parts later on. So once they’ve polished off one seed, they’ll move to the seed next to it. So you can end up losing the entire crop if the population is high enough."

In addition to wireworm- and soilborne disease-induced damage, studies have also shown wheat nematodes can interact synergistically with Rhizoctonia to further impede crop development. In fact, certain cropping systems, such as no-till, can accelerate that interaction to cause higher levels of crop destruction. In the Pacific Northwest, Paulitz and Schroeder observed wireworm and nematode symptoms similar to Rhizoctonia bare patch.

“Wireworms feed on the crown of the crop, attacking seeds and root systems, while lesion nematodes feed on the crop roots. The nematodes can even get inside the roots. We can hypothesize that nematodes provide more wounds for the fungus to get in," Schroeder said.

“Soilborne diseases, nematodes and insects like wireworms are driven by cropping practices, and therefore there is a lot of concern with direct-seeding, especially with the increasing wireworm problems lately," Paulitz explained.
To make matters worse, crops experiencing weather-related stress, such as drought or excess moisture, are even more vulnerable to damage and reduced yields. “Crops under weather-related stress react to attacks in various ways. Much of it relates to the speed of growth of the host. If the host is growing more slowly under cool conditions, there is more chance of damage by the fungus," Paulitz noted.

Roots are unique in that it can be difficult to monitor their health until undesirable symptoms appear above ground. While solutions to unfavorable interactions between soilborne pathogens, root-feeding pests and uncontrollable weather stressors are gradual and limited, they can be effective and profitable in the long run. One viable solution is to plant winter wheat within seven to 10 days of the first freeze – planting any earlier will put the crop at risk of early-season wireworm feeding. Because wireworm damage occurs primarily in the spring, during its cool, moist weather, careful consideration of seed treatment insecticides is important before planting spring wheat. Ultimately, the best way to confirm whether wireworms pose a threat is to scout before planting.

Growers increasingly understand the value in protecting their seed and profit potential through use of a top-performing seed treatment. A combination of seed treatment fungicide and insecticide, such as Dividend Extreme seed treatment fungicide and Cruiser seed treatment insecticide, can help cereal growers effectively protect crops against Rhizoctonia and Pythium, as well as other root rots and nibblers like wireworms. This pair safeguards crops as it stimulates plant growth and increases crop vigor, even under stressful conditions.

New Product in the Pipeline

Additionally, a new, experimental seed treatment fungicide from Syngenta is expected to be registered in 2012. Its formulation contains a new mode of action, which will offer an unmatched level of disease protection for stronger, more powerful roots and greater profit potential for growers. When it comes to battling the tough-to-detect soilborne diseases and insects, awareness of their presence and knowledge of field history are keys. Implementing proactive, protective measures, such as seed treatment applications, can also help alleviate hindrances to root health and crop productivity.

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