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Fight pathogens with right tools

Kyle Okke picture of White Mold and Goss’s Wilt.
ALL IN THE DETAILS: Farmers need to diagnose plant issues in the early stages to properly treat diseases such as white mold and Goss’s wilt.
Ag Mafia Alley: Know how to combat disease-causing plant pathogens in your crops.

What an amazing difference a year can make — from just last year’s historic drought to this season’s surplus moisture. The same difference could be said about weeds.

Last year, our pain mainly revolved around weed control, due to dry air coupled with extreme heat that hardened off weeds and left them unable to absorb any applied chemistry. But ask any of us about weed control now, and we’ll be hard-pressed to gripe about any major issues for this year’s growing season.

Why is there such a difference this year? We’d love to say it’s your local agronomist making great recommendations, which could be part of the reason, but excellent growing conditions also take some credit.

Excellent growing conditions are fueled by adequate soil moisture (to surplus, in many circumstances) with high humidity. This season every plant is loving life and growing at a breakneck pace. Unfortunately, more than plants enjoy this weather, and pathogens are lurking in the shadows ready to rear their ugly heads when the timing is right. These disease-causing plant pathogens are waiting for the right moment to “make a hit” and infect your growing crop.

Primer on pathogens, disease

Plant diseases such as white mold and Goss’s Wilt do not just magically appear in a crop if conditions are right; it takes a pathogen to infect the plant and cause the disease. There are three main types of plant pathogens that infect plants: fungal, bacterial and viral. Knowing the type of pathogen will dictate how you can manage it. For example, using a fungicide to cure a bacterial infection won’t work.

Let’s talk about these diseases and find why it’s important to know what type of pathogen is being dealt with:

White mold. This disease is caused by the fungus Sclerotinia sclerotiorum, which infects many broadleaf crops in North Dakota, including dry beans, canola and soybeans. The disease is exactly as described — a white mold that consumes plant tissue, cutting off the plant’s vascular system and causing premature death to parts of the plant affected. This, as you would guess, impacts yield severely.

The only way to stop this disease is to prevent it from happening. This requires a fungicide applied during the flowering stages of crop growth. The fungicide must be applied specifically to the petals of the flowering crop where the pathogen will be.

Sclerotinia sclerotiorum attaches to flower petals, and as the petals senesce, some fall onto other parts of the plant. The flower petal serves as a medium for the spores of S. sclerotiorum to germinate, and it will initially feed on the decaying flower petals. Once it has consumed that much, it keeps growing and consumes live plant tissue, even if it has been sprayed with a fungicide.

Therefore, it’s important to apply fungicide early during flowering stages of a crop — at 30% bloom on canola, and R1 for both soybeans and dry beans.

Goss’s wilt. The pathogen Clavibacter michiganensis, a bacterium, is to blame for infecting corn and causing this disease. Lesions develop and look like other fungal corn diseases and will be often misdiagnosed. A fungicide will simply not work to cure this disease, and no true antibacterial agents exist to apply and stop it. Rather, cultural practices such as rotations away from corn and choosing corn hybrids with genetic resistance to the disease are the best lines of defense.

Keep good records of which fields and hybrids you planted. If you experience Goss’s wilt, plan for a rotation away from corn and look to plant more tolerant corn hybrids next year.

Understanding a disease and its causal pathogen can help shed light on how to manage it. Just as the saying goes, “You don’t show up with a knife to a gun fight,” farmers need to understand they can’t apply a fungicide to cure a bacterial disease. Knock out these plant diseases by treating effectively.

Okke of Dickinson, N.D., owns Agile Agronomy and is part of Ag Mafia.

TAGS: Crops
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