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Poultry manure and potato early die

Potato Early Die complex (PED) has been a problem in North America for many years, devastating potato crops and reducing yield. “It’s caused by a soil-borne fungus, known as Verticillium dahlia,” explains Dr. Marisol Quintanilla, a nematologist working on a solution at Michigan State University.

Quintanilla explains that the fungus is able to infect potatoes on its own. However, when it gets help from a microscopic roundworm known as the Pratylenchus penetrans nematode, the infection can spread more rapidly. “The fungus doesn’t need the nematode in order to infect the plant,” she adds, “but the nematode helps, because it burrows into the plant, makes a wound, and introduces the pathogen into the plant.”

The fungus that causes PED seems to do well in cooler weather, and in climates where the soil is moist. It’s a problem in the northern parts of the U.S. and Canada. “This includes Michigan, Idaho, Oregon, Washington and a lot of the states in the Pacific Northwest,” adds Abigail Palmisano, a graduate student who works with Quintanilla at Michigan State University. “These are the areas that get a lot of rain.”

When PED hits potato crops, Palmisano says that up to 50 percent of the yield could be lost.

The infection causes wilting and yellowing in the lower parts of the leaves, Palmisano adds, and stunts the growth of the infected plant. “And if you open a potato plant,” she says, “You’ll usually see a ring in the stem. It’s a brown discoloration of the vascular system, which is also visible in the potato tuber.” An infected potato is still safe to eat, which means that an infected crop doesn’t have to be destroyed. The potatoes can still be harvested and sold. The problem is that the yield can be greatly reduced, which impacts the bottom line of North American producers. “The potato is an important plant for the economy,” adds Quintanilla. “So if the yield is cut by 50 percent, that’s a bit deal.”

One of the challenges with PED, according to Palmisano, is the fact that the fungus is especially hearty. “It can live in the soil for up to 20 years, and the potato field can be fine,” she explains. “It can be sitting in wait before infecting the plants, and farmers won’t know until it’s too late. Some growers will mistake [the infection] for early maturation.”

New research
Quintanilla and her team recently received a $750,000 grant from the USDA’s National Institute of Food and Agriculture to develop and evaluate sustainable methods of managing PED. One of Quintanilla’s graduate students, Luisa Parrado, helped write this grant.

As a nematologist, Quintanilla and her team will be using the grant to fund studies designed to find ways to deal with Pratylenchus penetrans, which is the specific nematode that is instrumental in the spread of Verticillium dahlia, the fungus that causes PED.

Example of discoloration caused by PED in a potato stem.

“This grant goes a little bit deeper,” Quintanilla adds, “because we found that some manures and manure compost had a significant effect on Pratylenchus penetrans. We wrote a publication on this and we wanted to understand why this is working.”

Their goal is to find out if compost formulas can be tweaked to make them more effective at controlling nematodes. “We found that the poultry manure blend that we were using from Morgan Composting, [a company in Michigan], was really effective at suppressing root lesions,” Palmisano adds. “We also prepared a compost blend, and found that it improved the yield and reduced the incidence of tuber vascular discolouration.”

The team discovered a combination of compost and more traditional chemical herbicides and fungicides helped reduce the population of nematodes. “However, none of the treatments were able to change the population, incidence or severity of the Verticillium dahlia fungus,” Palmisano adds.

Poultry manure is key
So far, research seems to be pointing at poultry manure as an especially effective ingredient in the composts that were most successful at controlling PED.  “We found that the lowest number of Pratylenchus penetrans (nematode) within the roots and soil was from the chicken manure application,” Palmisano explains. “It also boosted the number of beneficial microbes in the soil, so we’re thinking that the treatment is killing the nematodes, but also boosting the soil quality and the plants’ vitality.”

Quintanilla has a theory as to why poultry manure is most effective. “We compared the different sources of manures that we evaluated. One was dairy manure, one was poultry manure, and one was a combination of dairy, poultry and wood ash. We found that effectiveness is correlated with the level of acetic acid and butyric acid, and that chicken manure and ash had higher levels of these compounds.” Chicken manure, also had an effect on the vascular discoloration in potatoes. “So even though the fungi was still growing in the stems, there was a significant reduction in the amount of potatoes that were discolored. The chicken manure was suppressing the speed of the growth of the fungi.”

The fungi was still there, she notes, but it would seem that chicken manure helped reduce the fungal growth, thereby preventing it from getting to the potato. “We don’t know how this is happening,” Quintanilla admits, “so we’re still looking at it. It’s a tough nut to crack.”

The secret sauce
Based on research done so far, it would seem that PED might be best controlled by the specific combination of dairy manure, chicken manure and wood ash found in a compost blend sold by Morgan Composting. Quintanilla says that she shared her insights with the company owner years ago, and that he based his formula on her recommendations, which included her advice to add chicken manure in the mix.

In theory, producers could make their own blend of dairy and chicken manure, mixed with wood ash order to combat PED, but there’s no guarantee it will work as well as Morgan Composting’s blend.

“In order to make a general statement like, ‘Chicken manure compost is effective at reducing root lesion nematode and potato early die,’ we need to be able to test compost from other companies. When we test other products, we will be able to make a more generalized statement that will have a more national impact.” •