Sustainable pest, disease and weed management

I’m off to the Southern Sustainable Agriculture Working Group Conference in a couple of days. I’m presenting Intensive Vegetable Production on a Small Scale. At the link you can view a version of the slide show with lots of bonus material! (It was hard to cut the show down to 75 minutes!) I also had a lot of material on sustainable management of pests, diseases and weeds which I couldn’t even fit in the handout, so I’m posting that here.

A ladybug on a potato leaf, looking for pests to eat Photo Kathryn Simmons
A ladybug on a potato leaf, looking for pests to eat
Photo Kathryn Simmons

Biointensive Integrated Pest Management

The goal of IPM is to deal with problems in a systematic and least toxic way. Biointensive IPM goes further in emphasizing non-toxic methods.

There are four steps of IPM: prevention, avoidance, monitoring and suppression.

Sustainable Animal Pest Management

  1. Prevention: Focus on restoring and enhancing natural balance and resilience to create healthy plants and soil, better able to withstand attacks. Maintain soil fertility, good drainage and soil structure; plant resistant, pest-tolerant, regionally adapted varieties; grow strong plants; practice good sanitation,
  2. Avoidance: The next stage is taking actions to reduce the chances of a specific pest taking over. These actions are also known as physical controls. All these methods reduce problems without adding any new compounds into the soil. Use good crop rotations, remove pest habitat, deter known pests, use rowcovers, ProtekNet, low tunnels, high tunnels. Provide habitat for bats, insectivorous birds, spiders, birds of prey and rodent-eating ground predators (snakes, bobcats). Physically remove pests by hand-picking, spraying with a strong water spray, flaming, vacuuming, or by using a leaf-blower to blow bugs into a collecting scoop; solarize soil in the summer to kill soil-dwelling pests, as well as diseases.
  3. Monitoring (is action needed?) : regularly inspect your crops, find out when conditions are right for an outbreak of a particular pest, set traps and lures (sticky traps and pheromone traps) so you know when pests arrive or hatch out. Identify the pests you catch, keep records each year. Be prepared.
  4. Suppression: When the established action level for a particular pest has been reached, and prevention and avoidance strategies have been exhausted, bio-logical, microbial, botanical and mineral control measures can be used to reduce pest damage of crops to an economically viable level, while minimizing environmental risks. There are four types of sustainable bio-intensive control measures to choose from, starting with the least toxic solution:
    1. Biological control involves either introducing beneficial predators or parasites of the pest species, or working to boost populations of existing resident predators and parasites.
    2. Microbial controls refer to the use of fungi, bacteria, and viruses to kill pests.
    3. Botanical control uses plant-based products for pest control. An example is neem oil,
    4. Inorganic (mineral) controls, also known as biorational disease controls, make use of oils and soaps.


A zipper spider on a tomato plant, catching anything that lands on its web. Photo Wren Vile
A zipper spider on a tomato plant, catching anything that lands on its web. Photo Wren Vile

Sustainable Disease Management

Diseases need a susceptible host and the presence of a pathogen and suitable environmental conditions. Plant pathogens can be soil-borne, foliar-borne, seed-borne, or a combination of seed-borne with one of the others.

A. Soil-borne pathogens can live in the soil for decades, so long crop rotations are needed. Club Root is one. Fusarium oxysporum and Verticillium dahliae are two soil-borne fungi. Fusarium survives a long time in soil without a host, and can also be seed-borne.

B. Foliar pathogens need foliage! They die in soil in the absence of host plant debris, so practice good sanitation. Late blight (Phytophthora infestans) is a good example of this type of disease: it does not carry over in the soil, on dead plants, the seeds or the stakes. Cucurbit angular leaf spot (ALS) bacteria (Pseudomonas syringae) overwinter in diseased plant material and on the seed coat

C. Seed-borne pathogens: Lettuce mosaic virus is an example of a disease in which the seed is the main source of the pathogen and if seed infection is controlled, the disease is prevented. Other seed-borne pathogens may start life as a foliar-borne or a soil-borne pathogen. Infected seeds will produce infected plants even in clean soil. Pathogens can infect the seed via several routes: The parent plant can become infected by drawing soil pathogens through its roots up into the seed; Pathogenic spores can float in on the air (Alternaria solani, early blight of tomatoes; Anthracnose fungus that affects nightshades, watermelon and cucumber); Insects that feed on the plant can transfer the disease (striped cucumber beetles vector bacterial wilt, which is caused by Erwinia tracheiphila); Insects that pollinate the plant can bring infected pollen from diseased plants.

Rolling biodegradable plastic mulch to prevent weeds, warm the soil and prevent splash-back which can spread diseases from the soil. Photo by Wren Vile
Rolling biodegradable plastic mulch to prevent weeds, warm the soil and prevent splash-back which can spread diseases from the soil. Photo by Wren Vile
  1. Prevention and Avoidance (cultural controls)

Apply good compost and maintain healthy, biologically active soils; Optimize nutrients and moisture for crop vigor;

Practice good soil management (eg timing of tillage) to preserve maximum diversity of microorganisms; Use rotations to minimize disease and improve the environment for natural enemies of diseases; Time your plantings to avoid peak periods of certain diseases; Practice good sanitation of tools, plants and shoes; Use seed hot water and bleach treatments; Plant locally adapted, resistant varieties; Provide good airflow; Use mulches to reduce splashback from soil to plants; Use drip irrigation to reduce moisture on foliage; Use farmscaping to encourage beneficial insects.

  1. Monitor crops for problems

Make a regular tour of your crops once a week to monitor growth and health. Keep good records. If you see a problem, identify it. Plant Diseases Diagnostic lab can help. The mere presence of a disease does not automatically require spraying. The economic threshold (ET) or action level is the point at which losses from the disease warrant the time and money invested in applying control measures.

  1. When control measures are needed
    1. Physical controls: Removing diseased plant parts, protecting vulnerable plants with rowcovers or sprayed kaolin barriers, mulching to isolate plant foliage from the soil, tool and shoe sanitation, soap washes for foliage, hot water or bleach seed treatments, and soil solarization to kill disease spores are all methods that reduce problems without adding any new substance into the mix.
    2. Biological controls: Beneficial animals and insects are more common in insect pest reduction than in disease control, but the use of milk as a fungicide qualifies as a biological control. Plants in danger of developing powdery mildew can be sprayed weekly with a mix of one volume of milk with four volumes of water. When exposed to sunlight, this is effective against development of fungal diseases.
    3. Microbial controls: Homemade microbial remedies employ liquids (simple watery extracts and fermented teas) made from compost. For a simple compost extract, mix one part mature compost with six parts water. Let it soak one week, then strain and dilute to the color of weak black tea. Fermented compost tea can deal with many maladies. If your strawberries are prone to Botrytis, apply fermented compost tea every two weeks, starting when the berries are still green. See ATTRA or the Soil Foodweb site for how to make fermented compost teas.
    4. Botanical controls: Using plant-based products to reduce disease. Neem oil, as well as being a pesticide, forms a barrier on foliage that prevents some fungal diseases from establishing. It degRolling biodegradable plastic mulchdegrades in UV light in four to eight days and must be reapplied if the disease organisms are still around. Like all broad-spectrum insecticides, neem can kill beneficials as well as pests, so caution is needed if it is used. Garlic can be used against fungal diseases: blend two whole bulbs of garlic in one quart (one liter) of water with a few drops of liquid soap. Strain and refrigerate. For prevention, dilute 1:10 with water before spraying; for control, use full strength. Kelp sprays are also used to generally boost the resistance of plants to pest, disease and weather-related problems. Biofumigation by incorporating Ida Gold and Pacific Gold mustards into the soil
    5. Inorganic controls, also known as biorational disease controls: These include Bicarbonates (baking soda) one teaspoon (5 ml) in one quart (one liter) of water, with a few drops of liquid soap as a spreader-sticker against fungal diseases. Oils and soaps copper and sulfur products, as part of a prevention program (not a cure). Several of these need to be used with caution if the plants and the planet are to survive the treatment.

Sustainable Weed Management

Weeds compete with crops for sunlight, water and nutrients, and can encourage fungal diseases by reducing airflow. Too-frequent cultivation to remove weeds can leave the soil more prone to erosion. Each tilling or deep hoeing stirs air into the soil and speeds combustion of organic matter. Most weeds respond well to nutrients, especially nitrogen. If you give corn too much nitrogen, even as compost, its productivity will max out and the weeds will use the remaining nutrients.

Remove weeds at their most vulnerable stage, or at the last minute before the seedpods explode —ignore weeds doing little damage. There are different types: annuals and perennials; stationary perennials (docks) and invasive perennials (Bermuda grass); cool-weather and warm-weather types; quick-maturing and slow-maturing types; “Big Bang” types (pigweed) versus “Dribblers” (galinsoga).

  1. Preventing weeds from germinating
  • grow vigorous crops adapted to the locality,
  • close spacings, leaving less space for weeds,
  • switch between spring and summer crops in rotation,
  • drip irrigation rather than sprinklers,
  • mulch to bury short-lived weed seeds
  • plant promptly after cultivation,
  • transplant rather than direct sowing,
  • Multiple cropping, relay planting
  • Cover crops, including no-till, reduced till
  • Encourage seed-eating birds, insects, worms, mice
  1. Reducing weed seeding
  • Reduce weed seed banks to 5 % of original levels when weeds are not allowed to seed for 5 consecutive years.
  • Timely cultivation, Mowing, Flaming, Grazing by cattle, chickens, ducks, geese
  • Using post-emergence organic weed killers: corn gluten, vinegar, flaming
We use flaming to kill quick germinating weeds in our carrot beds. Photo by Brtitany Lewis
We use flaming to kill quick germinating weeds in our carrot beds. Photo by Brtitany Lewis
  1. Reducing seed viability
  • Most weed emergence happens within two years of the seeds being shed.
  • Seeds lying on or near the soil surface are more likely to deteriorate or become food for seed predators than buried seeds, so delaying tillage generally reduces the number of seeds added to the long-term seed bank
  • If they do not get eaten, dry out or rot, seeds on top of the soil are more likely to germinate than buried seeds.
  • Small, short-lived seeds of weeds with no dormancy period, such as galinsoga, will almost all die within a year or two if they are buried a few inches. Till and mulch to bury short-lived weed seeds
  • Longer-lived seeds (pigweed, lambsquarters, velvetleaf) if buried, may remain viable and dormant for years
  • Avoid deep tillage if you have long-lived-seed weeds
  • stale bed techniques draw down the seed bank in the soil
  • Solarization
  1. Reducing the strength of perennial weed roots and rhizomes
  • Apical dominance: when a rhizome grows a shoot, chemicals from that shoot prevent other nearby nodes from sending up shoots.
  • On long rhizomes, after a certain length, the dominance effect is too weak and another node can grow a shoot.
  • When rhizomes are cut into pieces during tillage, the apical dominance is lost and each piece can grow a shoot
  • But such shoots may be weak – Cultivate again before the new shoots have grown enough to send energy back to the roots, or pull out the pieces to dry on the surface: the depleted pieces of root or rhizome may die.
  • It’s more effective to wait time until the new top growth has drawn down the plant’s reserves (in the roots) before hoeing or pulling, than to go almost daily after every sprig.
  • Removing top growth whenever the weeds reach the three- to four-leaf stage can be most effective