Using Mustard to Reduce Soil Pests in Vegetable Beds

Cover crops such as yellow mustard can improve soil quality while simultaneously suppressing weeds non-toxically and loosening heavy, compacted soils.

Brassica cover crops containing mustards and/or rapeseed can effectively inhibit the growth of pigweed, hairy nightshade, puncturevine, green foxtail grass and barnyard grass. Once in place they can be terminated in spring by spraying with an herbicide, or by mowing and/or tilling before they go to seed.

Weed Suppression

Under pressure from intense weed pressure, sunlight and nutrients become scarcer for other uses; stems of young vegetables become choked out; disease-causing organisms flourish; weeds that germinate from roots, rhizomes, tubers or seeds become even harder to eradicate.

Mature cover crops provide competition against annual weeds that sprout from seed, making weed control more efficient than using either grasses or legumes alone. A mixture of grass and legume cover crops (such as buckwheat, sorghum-sudangrass and various millets) works especially well at protecting from annual weed invasion.

Light cultivation, flame weeding, and hand pulling are effective tools for controlling most annual weeds. For tougher ones, consider using a hoe with a wide blade such as an Asian-style hoe, hand cultivator or tall solid-blade hoe to get the job done.

Integrate a high-grade compost or manure into the soil two to four weeks before planting vegetables using the “stale seedbed technique.” This brings weed seeds closer to the surface and accelerates early germination. After adding in organic matter, use light cultivation techniques to kill any newly germinating weeds; tilling, hoeing or light cultivation combined with post-emergent or organic herbicide may help accomplish this task effectively.

Weed Attractant

Brassica cover crops (such as mustard ) contain high concentrations of glucosinolates that act as natural soil fumigants when cut or tilled into the ground, discharging chemical fumigants that suppress many forms of soil pathogens like fungi, nematodes, and weeds.

Due to this reason, many vegetable growers utilize mustard-based green manures as an effective alternative to fumigation. A SARE-funded study on potato cropping systems demonstrated that winter rape and white mustard significantly decreased incidences of Rhizoctonia root rot and Verticillium wilt more effectively than fumigation alone.

As fall cover crops, mustard species planted as fall cover crop are capable of being managed to winterkill and provide a soft seedbed, with minimal or no fertilization needs. Furthermore, they help with weed suppression while adding organic matter back into the soil – though only some mustard species overwinter in cold climates – some like rapeseed and arugula overwinter in most zones, making them inappropriate candidates for fall planting.

Weed Killer

Some of the most damaging pests threatening vegetable crops include leaf chewers, fruit feeders and worms. Preventing damage through early planting, thinning fruit before it matures and covering beds with row covers are effective strategies for mitigating this damage from these harmful insects. If problems do arise, picking off and drowning caterpillars as soon as they appear and spraying Bt (Bacillus thuringiensis) spray can also help significantly.

However, using herbicides can harm soil organisms and pollinators that play an essential role in plant health. Therefore, only resort to using these chemical solutions when necessary – and with caution. Weedkillers come specially tailored for certain weeding tasks – selecting and timing out one that matches up will produce optimal results in your garden. It is also vital that they be applied during calm conditions to minimise drift onto desirable plants; covering your garden plants with tarps or buckets to further prevent spray damage is highly advised if possible!

Biofumigant

Mustard can be used as an effective biofumigant to control root-knot nematodes in vegetable beds. Mustard plants produce large quantities of isothiocyanates (glucosinolates), which have proven effective at killing root-knot nematodes during glasshouse and raised bed trials. When decomposing and being integrated back into the soil, mustard plants release these isothiocyanates into the environment similar to chemical fumigants like methyl bromide. Mustard greens and some brassica cover crops (oilseed radish/rapeseed/rapeseed) make good choices for this application; oilseed radish/rapeseed/’Caliente’ mustard need long growing seasons to produce enough biomass for suppression purposes.

Farmers are planting Pacific Gold and Caliente mustard varieties late summer as a green manure and biofumigant, using them as winterkilling ground cover around 25 degrees Fahrenheit. Mustards can be planted together with oats or rye to increase biomass and glucosinolate production and then cut back prior to flowering/going to seed, thus keeping more glucosinolates in the ground longer to act as biofumigant.