Black Patch Disease
Causing Foaming, Slobbering, & Excessive Salivation In
|This is a fungal disease caused by Rhizoctonia leguminicola occurring in the entire upper part of the red or crimson clover. The lesions are blackish brown and irregular shaped on the leaf. They soon fuse mutually and become large lesion which covers the whole leaf. The black and fluffy sclerotia are produced in the center part of the lesion. Black hyphae extends to the entire plant when occurring severely and cause plant death. Hyphae is the part of the fungus that feeds, grows, and ultimately may produce a mushroom or some other kind of reproductive structure. It is a threadlike tubular filament possessed by many fungi that function in nutrient absorption and transfer . It often looks white and web-like.|
Excessive salivation, characterized by drooling or frothy saliva around the lips, may be caused by a variety of things including chemical irritants fungal toxins, virus and bacterial diseases affecting the mouth, teeth problems, choking caused by esophageal obstruction, and various toxic or injurious plants. Grazing animals that eat sharp grass awns, spiny plants such as the prickly pear cactus or those with burs such as burdock and cocklebur may injure the oral mucosa. Some common grasses such as foxtail barley bristle grass and sandbur have seeds with sharp awns that can become embedded in the tongue and gums of animals eating them. Initially excessive salivation may be noticed, but in time the grass awns or spines that are imbedded in the mucosae create large ulcers. The awns are not easily visible in the ulcers because they become embedded in the granulation tissue filling the ulcer. It is not uncommon for some sharp grass awns to penetrate the skin of animals, migrate through the tissues, and act as a foreign body causing abscesses and draining wounds far from the site of penetration .
Profuse salivation has been observed in horses, llamas, and other livestock eating clover or alfalfa pasture or hay that is infected with the fungus Rhizoctonia leguminicola. The mycotoxin responsible for the "slobbering" that animals exhibit has been identified as slaframine, an indolizidine alkaloid produced most commonly by the fungus R. leguminicola growing on red clover. Slaframine is chemically similar to the alkaloid swainsonine produced by plants of the genera Astragalus and Oxytropis that are responsible for causing locoism. Under wet or humid conditions the fungus grows on the leaves producing black or brown spotting. After they eat the fungus-infected clover for several days, horses begin to salivate excessively and lose weight; pregnant mares may abort if they continue to consume the infected clover. Recovery occurs rapidly once horses are removed from the infected hay. Problem pastures can be used for animals if they are mowed, the affected hay is removed, and the regrowth has no brown spotting on the leaves.
Professor of Agronomy and Forage Crops Specialist - Purdue University
1150 Lilly Hall of Life Sciences
West Lafayette, IN 47907-1150
The Slobbers - Black Patch Disease
The slobbering is associated with black patch disease caused by Rhizoctonia leguminicola. The specific causal agent is slaframine which is an indolizidine alkaloid and a metabolite of Rhizoctonia leguminicola. Conditions were right for its development this year, rainy conditions and high humidity.
Interestingly, the compound does decrease in red clover hay while in storage, but only after a period of time. One study sites a decrease in 10 months of storage from 50-100 ppm to 7 ppm.
Reading about the associated biological effects in Peter Cheeke's "Natural Toxicants in Feeds, Forages, and Poisonous Plants" book makes one raise their eyebrows as to why we even use potentially infectious clovers at all. In cattle, concerns include excessive salivation, eye discharge, bloat, frequent urination, watery diarrhea, reduced milk production, weight loss and abortion. Other things noted include increased pancreatic flow, bile flow, and gastric acidity, and decreased heart rate, cardiac output, respiration rate, body temperature, and metabolic rate. With use of guinea pigs as an assay animal, the LD50 was less than 1 mg of slaframine/kg (1 kg=approximately 2.2 lbs.) of body weight.
Applying some mathematics and assuming a guinea pig and horse have a similar lethal dosage response, a 100 ppm slaframine forage fed to a horse consuming 25 lbs. of dry matter is equivalent to 11.35 mg of slaframine. Assuming the horse weighs 1000 lbs., this is a dose of .025 mg/kg of body weight, much less than the lethal dose rate found in the guinea pig experiment.
So do you get rid of the clover? If you truly don't enjoy your llamas or horses because of the slobbers, maybe so. Keep in mind, that you may not see slobbers to the same extent each year - it will depend on the weather.
You need to balance the positives and negatives for the use of red and white clover in your pasture. There are many positives (forage quality improved, more summer pasture with use of red clover, no N fertilizer needed for the grass component of the pasture) when legumes are a part of the pasture. Is this worth more than the negative issue of slobbers? This is a judgmental call that I think you need to consider.
Maybe other type grasses should be the choice when seeding your next hay and pasture fields?
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