Crab meal may hold answer in battling crop disease

QUEENSTOWN, Md.  — Growers trying to suppress disease and break down sclerotia in their fields may find some assistance from a unique treatment option: Crab meal.
A group of University of Maryland researchers evaluating soil amendments and cover crops in 2015 to see how they impact Botrytis cinerea survival and soil health determined that a combination of compost, crab meal and cover crops can suppress pathogens, boost nutrients and discourage weeds. Sclerotia are hardened,resilient overwintering structures for Botrytis, which causes gray mold, and affect many crops such as strawberry plants.
“If you added some of this crab meal, it did increase your nitrogen, phosphorous, it did increase your pH if that’s what you were going for, and it does break down these (sclerotic) survival structures,” said Kate Tully, an assistant professor of agricultural ecology. “This is sort of a new idea we had.”
Tully and colleagues Cassandra Swett and Emmi Koivunen, both now working in California, studied a series of treatment options at the university’s Wye Education and Research Center from 2015 to 2016. Crab meal — discarded, dried and ground crab shell — has been used in an agricultural context abroad and around locations with booming seafood industries such as Maine. Its use has escaped the Chesapeake Bay region, however.
“Maryland, interestingly, there isn’t really a market yet. You can’t really buy crab meal,” Tully said. “One of the ideas we had is, well, you have a heck of a lot of crabs in Maryland, so this could be a potential business opportunity.”
Treatments included leaving the field fallow, different leaf compost (Leafgro) amendments, leaf compost and with a dwarf rape cover crop, crab meal, and crab meal with leaf compost and a caliente mustard cover crop.
Applications of Leafgro essentially followed the manufacturer’s recommendations. After amendments cover crops were planted, six mesh bags with 10 sclerotia samples were buried in each field plot for months before they were recovered and evaluated.
“If they weren’t broken down then that would mean that there wasn’t really any suppression of that pathogen,” Tully said. “But if they were broken down that would mean that there was some biofumigation properties there and they were breaking down (pathogen) survival structures.”
After five months, the combination of leaf compost, crab meal and caliente mustard worked best among treatment applications.
About half of one sclerotia sample out of 10 survived inside bags buried in the fields.
That combination also had the highest soil phosphorous level throughout the study. In that treatment, 69.7 tons per acre of Leafgro was applied in fall and spring, nearly 3,000 pounds of crab meal per acre was applied in fall and nearly 6,000 pounds in the spring and caliente 199 was planted in the spring.
But crab meal alone broke down sclerotia in the soil most effectively.
“It basically boosts the microbial community that breaks down the (sclerotia),” Tully said.
According to a report summary, “it may be advisable to apply a combination of compost, crab meal, and cover crops in order to decrease pathogen survival in soil while increasing soil nutrients and discouraging weeds. In our study, the leafgro and dwarf rape treatments… seemed to stimulate the growth of Botrytis cinerea sclerotia; thus it seems crucial to add crab meal (or another chitinous material) alongside composts and cover crops in order to diminish this effect.”
The study did not evaluate the treatments on actual crops, so more research must be done to determine whether they negatively affect crop growth or yield, the summary said. Because crab meal appears to boost soil pH, it might not be suitable for crops that like low-pH soils.