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Some mid-September sown seedbeds in Toombs County growing nicely.

Over the last few weeks, I have been traveling around the Vidalia area with county agents to check on onion seedbeds. It has been a relatively quiet start to the season on my end, which is usually a good thing. All the seedbeds we’ve visited look really good overall. Perhaps the most noticeable difference from last season has been the cooler, more favorable temperatures. Not cool enough for the rattlesnakes to stop moving, however.

Toombs County Extension Agent Jason Edenfield holds up a Diamondback Rattlesnake that crossed our path at McLain Farms last week. Daniel Jackson was visiting us from Athens and was witness to what has seemed like a common sight lately.

2020-2021 Variety Trial

The seedbeds at the Vidalia Onion and Vegetable Research Center were sown on September 22. They are coming along nicely and will probably be mowed in the next week or so. This year, we planted 50 different varieties to evaluate for yield and flavor. The county agents were a big help this year as always with planting.

50 varieties were sown this year on September 22nd
Tattnall County Agent Derrick Bowen having an important onion talk with Toombs County Agent Jason Edenfield.

While it has been relatively quiet with any onion problems so far this year, there are some out there that I want you to be aware of going into the start of transplanting. Most of these are small scale minor issues overall but i think they are worth sharing.

Nutrient Deficiencies

I’ve run across a couple of instances of suspected nutrient deficiencies. In both cases, the problem seems to have been corrected with an application of Epsom Salts and/or complete fertilizer. This leads us to believe the issue may have arose from the leaching of nitrogen or sulfur. These nutrients are mobile in the soil and can leach with irrigation. This is not uncommon in onions, especially when they are young and do not have extensive root systems to gather these nutrients.

Although very subtle when looking at individual plants, the light green color of the new leaf (center) along with some tip yellowing gave this onion field a “yellowish” cast and something looked “off”. This was likely from a slight deficiency in either nitrogen or sulfur.

In both cases I have seen this year, we believe that excessive irrigation may have caused the problem. However, I use the term “excessive” loosely because sometimes there is not a way to avoid it. We often have to water young seedbeds everyday on very sandy soils to help them establish roots and grow. Growers will also often have several staggered plantings under the same pivot, so they are having to continually water seeds that have just been planted. Older seedlings that may not necessarily need water will get it to help out their younger counterparts emerge and become established.

Bacterial Disease

In seedbeds, bacterial disease is most often caused by the pathogen Xanthomonas axonopodis pv. allii. This pathogen will often start out as small lesions that have a water-soaked appearance, such as this one pictured above. If conditions are favorable for development, it can progress up or down the leaf. The bacterial pathogen that can cause Center Rot, Pantoea spp., is often isolated from seedbeds with similar symptoms as well.

In seedbeds, bacteria (as opposed to fungal pathogens) cause the majority of disease issues that we see each year. I have received very few reports of disease in seedbeds this year. However, we have observed some isolated issues. Xanthomonas leaf blight is the most common, and Pantoea spp., the pathogen responsible for center rot, can also be found in seedbeds. Water-soaked lesions are common symptoms for both of these pathogens in seedbeds. It is often seen as seedbeds become older and the canopy becomes more dense, and is often noted during extended periods of leaf wetness, such as when rain events occur that prevent drying of the canopy for several days.

As bacterial disease such as Xanthomonas progresses, it will cause water-soaked lesions over large portions of onion leaves and tips, like the leaf pictured here.

As our seedbeds continue to grow, 3 things to keep in mind to about bacterial disease in seedbeds:

  1. We will likely see some bacterial disease as the plants get bigger and the canopy gets more dense. Rain events may trigger the onset of this.
  2. The only treatment option for control of bacterial disease is fixed-copper compounds (e.g. Kocide 3000) tank-mixed with an EBDC fungicide (e.g. Manzate). These should be applied preventatively.
  3. Be judicious with your nitrogen applications and irrigation. Don’t overdo it. This can cause problems or make a problem worse.

Stubby Root Nematodes

Symptoms of Stubby Root Nematodes on plant roots, 6 weeks of age. These seedlings roots are very forked with short and stubby roots. Affected plants will often begin to “bulb” prematurely.

I think that over the last 2 or 3 years, we have become more aware of nematode problems in onions. Recognizing this issue is important, because we can’t get a grip on controlling without knowing what our problem is. Most growers are aware now of the issues that Stubby Root Nematodes can cause in onions. We see it more often in seedbeds, and have found some this year.

This is a picture of a healthy onion plant root system at 6 weeks of age.

It is too late to do anything about a nematode problem at this point. I know that many growers are using Telone to help with Stubby Root Nematodes. We know that Telone is a useful treatment for them, and are hoping to have more answers about the best way to use it in the future. I want to ask all growers to take a minute and think about your crop rotations. Sometimes, rotation is the only way to avoid serious nematode problems. Ask yourself these questions if you have problems:

  1. Are my seedbeds in the same field that they were last year?
  2. Are my seedbeds grown in the same field that transplants grew last year?
  3. Are my seedbeds on land that was recently in another crop that can be a host to to Stubby Root nematodes, such as corn or soybeans?

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