Crop Rotation, Pests & Disease
"An ounce of prevention is worth a pound of cure." - Benjamin Franklin
Garlic is a natural repellent for many insects and animals but garlic can come with it's own pest and disease issues. The harmful stem and bulb (Bloat) nematode is one of the most destructive pests to garlic worldwide and can destroy a crop in one season. It commonly attacks garlic and onions but may attack all members of the Onion Family (Allium) as well. Most infestations happen because an afflicted clove from seed garlic is unknowingly planted. It's not always apparent above ground when garlic plants are infected by way of premature yellowing of leaves or stunted growth for example, because that could point to several other issues that may be benign in nature. Suspicions of infestation can arise once the bulbs are harvested and show beginning signs of deterioration immediately or very soon after. Once introduced, the stem and bulb nematode persists in the soil for many years and will damage any future 'clean' garlic that's planted until the soil is corrected. Plots must go through a rigorous and lengthy eradication process before replanting Alliums can even be considered.
The best line of defense to prevent infected garlic crops and soils is to not plant infected seed. By choosing clean seed from a farmer that adopts the strategies below in addition to using preventative measures yourself, you chances of having a nematode problem are very small.
Crop Rotation: Best farming practices to prevent nematode infestation is by adhering to the recommended 4 year crop rotation for garlic plots. This includes not planting onions or any other Allium member before or after a garlic crop. Alliums are a host plant for harmful nematodes.
Sanitation: Sanitize all tools and farm equipment used in the garlic plots. Do not allow cross contamination by using tractor implements or hand tools that you've used in garlic plots to be introduced into new fields without sanitizing first. This is tedious and redundant and may have to be done often but it's a necessary practice that needs to be put into place.
Garlic Waste: Do not put your garlic waste (leaves, root trimmings, culled bulbs/cloves) back into your fields, ever. Nematodes love to live a long time on that dried organic material and will be introduced to your soils that way. Even if your garlic is clean you should trash or burn the garlic trimmings as a preventative measure. As gut-wrenching as it may feel especially if you are a commercial grower, once you have a suspected nematode infestation the right and ethical thing to do is to test your garlic crop and soils and if confirmed positive, you really should trash or burn your seed garlic. Or, make it clear it's only appropriate for culinary purposes. Do not pass on the problem.
Composts and composted manures: Ensure that the composted materials you bring home to your gardens and fields is clear of pests and disease by having it tested before amending your soil. If you choose to use your own livestock manure be sure that that the manure is appropriately decomposed which can take several months.
Cover crops: As a preventative, plant mustard seed every season into garlic plots that are out of rotation. Till the mustard into the soil before it goes to seed. Mustard seed is a very hot, aggressive fumigant to fight the presence of harmful nematodes among other harmful soil pests, and will give your fields a big boost of healthy nitrogen.
Critters: Rare is the animal that is attracted to garlic, however, pocket gophers will feast on your crop as if you planted it just for them. Speedy trapping of these creatures will ensure that all your garlic lives to see harvest.
We utilize a 4 year plot rotation for our garlic crops. In September 2021 we broke ground on a new, fresh field for Fall planting! This new field will accommodate our next 4 seasons of rotational garlic growing. As the new owners of this farm that had existing commercial garlic plots in place, we decided the best course of action was to start fresh going forward. Under Tilth requirements for organic certification we are required to grow cover crops on all plots that are not in use each year. We will always use mustard seed on our off years. Also required, is sanitation of tools and equipment used in the garlic fields. We do, and often! Even the tractor tires and implements are sanitized before going into our dedicated garlic fields. To make it easier we keep specific buckets, shears, shovels, rakes, gloves, and gopher traps dedicated solely to the garlic and their fields. All of our garlic trimmings go right into a burn barrel. The compost and manure inputs come directly from our farm and our livestock, and are appropriately seasoned. The Tilth requires that all compost inputs are approved prior to amending the soil. The pocket gophers are our nemesis- please send help!
At the end of each harvest we send out a sample of soil and garlic bulbs to test for the presence of nematodes before we offer our garlic for sale. It truly is a small price to pay for peace of mind because we care. The majority of our planted seed will be our own from prior harvest. When we order organic seed garlic to increase our varieties we only purchase from farms that utilize 4 year crop rotation and/or undertake nematode testing as well. We also test incoming seed garlic from other farms before it goes into our fields. As a commercial grower the last thing we want is to ruin our garlic, our fields, and our livlihood -or- be in the hot seat for ruining someone else's.