29
Mar
Slug Killer Chemical Found to Hamper Growth of Garden Veggies
(Beyond Pesticides, March 29, 2023) A commonly used slug killer known as metaldehyde can hamper the growth of garden vegetables. This finding, published in the journal Scientific Reports, provides a helpful reminder for gardeners to seek out non and less toxic management approaches as spring comes into full swing and pests arrive. While slugs can be devastating to seedlings this time of the year, some simple approaches can help reduce pest pressure while maintaining the quality and integrity of one’s garden plot.
Metaldehyde is a molluscicide that is applied through a bait, causing slugs to expel mucus and completely dry out. It has been in use since the 1940s, but like many pesticides from that era, there are a range of hazardous impacts that were not adequately studied at the time and are only beginning to be understood today. In mammals, ingestion of the chemical has been linked to neurotoxicity, including tremors, loss of coordination, rapid breathing and heart rate, vomiting, seizures and even death. Although humans are less likely to eat the baits, these risks are particularly pronounced for children and pets.
Data on the impacts this material poses to plant growth is few and far between. To remedy this, and better understand whether metaldehyde could impact yields, scientists utilized Allium cepa, or onion plants, as a model test organism.
Onion bulbs were purchased and divided into four different treatment groups with increasing levels of metaldehyde exposure (in the form an aqueous solution), as well as an unexposed control group. Scientists observed growth patterns and the genotoxic impacts of exposure to the material.
While the control group saw 100% germination success, this rate decreased as metaldehyde concentrations increased. It follows that the highest rate of exposure resulting in the greatest inhibition of plant growth. Adverse impacts were also seen to root growth and root elongation, and onions exposed to the chemical recorded a consistently lower weight than those unexposed. These were merely the apparent physical impacts; metaldehyde also resulted in statistically significant DNA damage to exposed bulbs. DNA fragmentation is seen in root tip cells, and effects are noted on the activities of antioxidant enzymes, indicating elevated stress levels in the plants.
“The results of this study highlighted the need for new and detailed studies on the undesirable effects of metaldehyde on non-target organisms, including humans,” the authors say.
Commercial slug baits should not be necessary in the garden. Although the National Organic Program permits the use of an alternative to metaldehyde, iron phosphate, in slug and snail control, its efficacy relies on a synergy between iron phosphate and a so-called “inert” ingredient known as EDTA. In 2014, Beyond Pesticides called on the National Organic Standards Board to delist iron phosphate slug products due to the risks that EDTA poses to soil organisms, as well its ability to contaminate soil, sediment and local waterways.
The good news for gardeners dealing with snail and slug problems is that management is still possible without these more toxic baiting products. Work to reduce moisture and consider the type of mulch that is being applied –straw can be an excellent mulch, but there are times in which its use can attract slugs. Never water at night, and consider tactics like drip irrigation in particularly damp, slug-prone areas as slugs are attracted to moisture. Hand-picking slugs out of the garden with a disposable glove and placing them into soapy water isn’t a favorite activity among any gardener, but it can be an effective way to reduce populations. Domestic foul can also be helpful at lowering slug populations but need to be closely monitored around growing crops.
There is evidence that effective biological controls are coming closer to commercialization. Researchers at Oregon State University (OSU) have been on the case for many years now, and made a promising discovery in 2020 when they found a nematode that effectively ‘liquified’ slug populations. The OSU research team also discovered that slugs can be attracted with simple bread dough. While that research utilized bread dough to attract and metaldehyde to kill, many traps and baits on the market, such as the Snailer, can work with bread dough and water without the need for additional pesticide, as they bar pests from exiting and cause the slug or snail to drown.
For more information on managing these problematic pests, see Beyond Pesticides ManageSafe webpage on least toxic control of snails and slugs.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source: Scientific Reports
Image Source: Wikimedia
