There is a common myth that lavender does not have any pests and can actually repel pests from the garden. This often means that pest management is the last thing a grower thinks about when managing lavender. The reality is that lavender has many insect and disease pests. Preventing them from becoming economically important pests should be one of the first things a grower thinks about when purchasing plants and preparing land. It should also be top of mind throughout the growing season.
Although in many years lavender has few economically important pests, when pests do start to cause damage there are few pest control products that growers can use to control them. The few pest control products that are available will work best when used to manage pests before they become economically damaging. Waiting for a crisis to think about pest management can result in major damage and an inability to get the problem under control.
The list of pest control products registered for use on lavender is available here: Lavender Pest Control Product List 2020
All pest control products registered on lavender were based on a registration on the Herb Crop Group. Crops are placed into different groups for the purpose of pest control product registration, and representative crops are designated for each group. Research conducted on the representative crops can be used to extend a product registration to all the crops in that group, which is what happened to attain the registrations on lavender. Different herbs have different pests, and crop group registrations can result in registration of products on pests that do not occur on lavender. As a result, some products that are registered for use on lavender are not listed here because the pest they control does not affect lavender. Below are some considerations for management of different pests of lavender using pest control products.
Phytophthora Root Rot: This disease is the most economically damaging pest on lavender, but there are no pest control products that are registered to control or suppress this disease. Management of the disease requires sanitation in the greenhouse, monitoring of transplants for symptoms, avoiding introducing it to the field, removal of infected plants and neighbouring plants, and most importantly, ensuring good drainage in the field.
Septoria Leaf Spot: There are no pest control products that are registered to control or suppress this disease. Since this is an airborne pathogen, it is impossible to avoid the disease. Management requires keeping plants healthy through proper fertility and irrigation and by promoting good airflow through the plant canopy.
General Root Rots: Both in the greenhouse and in the field, lavender can be affected by several root rots other than Phytophthora such as Fusarium, Rhizoctonia and Pythium. Just like Phytophthora, ensuring soil is well-drained is the most important consideration for managing these diseases. In transplants, Rootshield HC is registered to suppress these diseases.
Molds: Both sclerotinia white mold and botrytis grey mold have been identified as pests of lavender. They would mainly occur under extended periods of high humidity and warm temperatures, which are most likely to occur in the greenhouse. Botrytis grey mold is often associated with dead or dying tissues and then moves over to healthy tissues from there, and is most likely to be an issue when there is physical damage to the plant such as pruning. It can also develop on cuttings before they root in the greenhouse. Management of these issues is usually not required in Ontario lavender, but where they become a problem there are products available for suppression of these diseases in both the greenhouse and the field.
Four-Lined Plant Bug: Four-lined plant bug (FLPB) is the most damaging insect pest that affects lavender in the field in Ontario. They can cause considerable aesthetic damage to the developing lavender flowers and render cut bundles unmarketable. Populations of FLPB can build up as the lavender field ages if left uncontrolled. While there are no pest control products registered for use against FLPB in lavender, insecticides applied for use against aphids may reduce populations if they are applied when the nymphs of FLPB are very small. This requires close inspection of plants, which may allow for a spot spray to reduce FLPB in a small area where populations are highest.
Garden Fleahopper: Garden fleahoppers can occasionally build up to damaging levels in lavender, especially on black plastic mulch. The extra warmth over the mulch may allow populations to develop more rapidly. Like FLPB, there are no pest control products registered specifically for garden fleahoppers, but insecticides applied for aphids may provide suppression of populations, especially at the nymph stage. Most of the time there are hot spots where the pest is out of control, and a localized application may be all that is needed.
Spittlebugs: Spittlebugs can be unattractive in a lavender field, but rarely cause economic damage and pest control products are neither registered nor required for this pest.
Aphids, Whiteflies and Thrips: These pests are mostly associated with lavender production in the greenhouse but can occur in the field if they are transferred there by infested transplants. Proper sanitation and the use of biological controls in the greenhouse can keep populations from getting out of control. If the application of pest control products is necessary, there are several products registered for control or suppression in both the greenhouse and the field.
Two-Spotted Spider Mites: The two-spotted spider mite (TSSM) is definitely a pest of lavender in the greenhouse. Extensive damage has been noted where there are no biological or chemical controls. The problem can easily be transferred to the field and can become established in hot and dry summers. Natural predators may start to suppress the pest outdoors over time and make the application of pest control products less necessary. Insecticidal soaps are registered for control of this pest in the greenhouse, and there are several biopesticides and conventional pesticides registered for control or suppression of TSSM in the field.
Organic vs Conventional: The principles of integrated pest management should be the same no matter how lavender is managed. Pests should be managed with cultural means as much as possible and the use of pest control products should be a last resort. Pest control products are permitted in both systems, but synthetic pest control products are only permitted in conventional production. Most of the products registered on lavender are permitted in organic production. However, each organic certifying body differs in what they permit for use. If you are organic or intend to be certified, consult with your certifying body to confirm what you are permitted to apply to your lavender.
Using Pest Control Products: Many lavender growers are unaccustomed to applying pest control products and may not know the rules around their use. Here are some main points to consider:
- All growers that intend to use a pest control product, including both organic and conventional products, must be certified by taking the Grower Pesticide Safety Course and passing a written exam before they are permitted to purchase or use the products. The course is offered by the Ontario Pesticide Education Program .
- The pesticide label is the law. You must read the label and follow all use precautions including rates, necessary personal protective equipment, buffer zones between the application area and sensitive habitats, number of applications permitted per year, restricted-entry intervals (REI) and pre-harvest intervals (PHI). Restricted-entry intervals are the amount of time workers must keep out of the application area before it is safe to re-enter. Pre-harvest intervals are the amount of time after application you must wait before harvesting the crop.
- Spray coverage is key to maximizing product efficacy. Whether you are using a backpack sprayer or a large boom, having the proper nozzles and pressure is important for ensuring all surfaces of the plant are covered. Many insect pests are protected under the leaves, so under leaf coverage is very important. Coverage is especially important for products that are only registered for suppression of the pest. For more information on spray coverage consult sprayers101.com.
- Avoid applying any pest control products during lavender bloom. Lavender promotes numerous pollinators, especially bees during bloom and any potential for harm of these pollinators should be avoided, even if the label does not specifically preclude it.