Alfalfa is an important forage crop grown across many regions for feeding livestock. However, these nutritious plants can fall victim to tiny yet destructive pests – spider mites. These sap-sucking mites can proliferate rapidly in hot, dry conditions and can wreak havoc on your alfalfa fields if left unchecked. Severe infestations stunt plant growth, reduce yields and ultimately kill the crop.
As an alfalfa grower, it is critical to control spider mites before they get out of hand. The key is to regularly scout your fields, quickly identify infestations and use integrated pest management (IPM) strategies combining various chemical and non-chemical methods.
Here is a comprehensive guide on how to effectively get rid of spider mites in your alfalfa crop.
Identifying Spider Mites in Alfalfa
-
Spider mites are tiny, about 0.5 mm in size with oval, transparent bodies and usually yellowish to greenish in color.
-
They colonize on the undersides of leaves and stems where they suck plant fluids,
-
Fine webbing on leaves is the most characteristic sign of their presence.
-
Leaves turn yellowish or bronze initially and then dry out and drop off with heavy infestations,
-
Use a hand lens to look for the tiny, slow moving mites on the plants. Watch for faint speckling on leaves as well.
-
Spider mite problems get worse in hot, dry weather exceeding 85°F.
Monitoring Alfalfa Fields for Spider Mites
-
Check alfalfa weekly by randomly examining leaves from the lower canopy.
-
Focus monitoring along field edges or areas with prior infestations.
-
Early detection is key – inspect closely with a hand lens before signs are visible to the naked eye.
-
Monitor more frequently during peak mite seasons in mid to late summer.
-
Record infestation locations and levels to target treatments.
Action Thresholds for Spider Mite Control
-
Treat isolated spots when 20-30% of plants show early stippling.
-
For more general infestations, use the following thresholds:
-
Before bud stage – 40% infested stems
-
Bud to first flower – 20% infested stems
-
After first flower – 50% infested stems
-
-
Treat promptly once thresholds are exceeded before mites disperse further.
Cultural and Biological Spider Mite Control Methods
-
Maintain healthy plant vigor through proper irrigation and fertility. Healthy plants better withstand mite damage.
-
Avoid excess nitrogen fertilization which can encourage mite outbreaks.
-
Cut early to remove heavily infested growth and prevent mites from spreading.
-
Remove any weedy vegetation from field edges that can harbor mites.
-
Consider conserving predatory mites, lady beetles and other beneficial insects that prey on spider mites.
Using Insecticides/Miticides to Control Spider Mites
-
Insecticidal oils like supreme or superior oil provide quick knockdown of mite populations when directly sprayed. But they do not provide residual control.
-
Insecticidal soaps such as M-Pede® are effective on contact but also don’t provide long term control.
-
Miticides/insecticides such as Abamectin, Bifenthrin, Zeta-Cypermethrin are longer lasting and control mites feeding on treated plants. But they can also kill beneficial insects. Use judiciously and rotate between chemical classes to reduce resistance issues.
-
For best results, make 2 applications 7-10 days apart to control newly emerged mites. Target undersides of leaves and achieving thorough coverage is key.
-
Read and follow label directions carefully for mixing concentrations, application rates, timing, pre-harvest intervals etc.
IPM Approach for Sustained Spider Mite Control
An integrated approach combining preventive cultural practices, conservation of beneficials, and timely miticide use when absolutely necessary provides the best long-term, sustainable spider mite management.
-
Start with field hygiene – remove any plants or weeds bordering your alfalfa crop that can act as sources of infestation.
-
Promote healthy, vigorous crop growth to withstand mite pressure.
-
Scout regularly and conserve natural enemies.
-
Use insecticidal oils/soaps or introduce predatory mites early before mite populations explode.
-
For severe infestations, apply targeted miticide treatments when action thresholds are met. Rotate chemical classes and use all labeled best practices to optimize control and prevent resistance issues.
Preventing Spider Mites in New Alfalfa Stands
You can take proactive steps to avoid mite issues when establishing new alfalfa fields:
-
Select more mite-resistant alfalfa varieties best suited for your region.
-
Thoroughly destroy any old alfalfa growth in the field prior to planting the new stand.
-
Carefully inspect any nursery stock brought in and treat as needed to avoid introducing mites.
-
Monitor new seedings frequently and act promptly at the first signs of infestation before mites multiply.
When to Call in a Professional
Spider mite management in established alfalfa requires diligent scouting, adherence to treatment guidelines and proper insecticide application and coverage – which can be challenging for growers to implement themselves.
Consult with professional crop advisors or custom applicators in your area who have the technical expertise and right application equipment to control mites in a timely, effective manner. This is especially advisable for severe infestations spanning large acreages.
The damage caused by uncontrolled spider mite infestations can be devastating to your alfalfa yields and profitability. By identifying and addressing issues early using a comprehensive IPM approach, you can protect your crop’s health and productivity.
Twospotted Spider Mite Gallery
-
Twospotted spider mite diapausing females on cherry (E. Beers)
- leaves covered with diapausing females
- Twospotted spider mite diapausing females on cherry (E. Beers)
- Twospotted spider mite diapausing females on cherry (E. Beers)
- Twospotted spider mite egg (E. Beers)
- an egg on a leaf
- Twospotted spider mite egg (E. Beers)
- Twospotted spider mite egg (E. Beers)
- Twospotted spider mite egg, larva, adult (E. Beers)
- an egg, larva and adult on a leav
- Twospotted spider mite egg, larva, adult (E. Beers)
- Twospotted spider mite egg, larva, adult (E. Beers)
- Twospotted spider mite larva and eggs (E. Beers)
- larva and two eggs on a leaf
- Twospotted spider mite larva and eggs (E. Beers)
- Twospotted spider mite larva and eggs (E. Beers)
- Twospotted spider mite adult and egg (E. Beers)
- adult and an egg on a leaf
- Twospotted spider mite adult and egg (E. Beers)
- Twospotted spider mite adult and egg (E. Beers)
- Twospotted spider mite adult male (E. Beers)
- an adult male on a leaf
- Twospotted spider mite adult male (E. Beers)
- Twospotted spider mite adult male (E. Beers)
- Twospotted spider mite chrysalis (E. Beers)
- chrysalis on a leaf
- Twospotted spider mite chrysalis (E. Beers)
- Twospotted spider mite chrysalis (E. Beers)
- Twospotted spider mite adult females (E. Beers)
- two adult females on a leaf
- Twospotted spider mite adult females (E. Beers)
- Twospotted spider mite adult females (E. Beers)
- Twospotted spider mite adult female (E. Beers)
- closeup of an adult female on a leaf
- Twospotted spider mite adult female (E. Beers)
- Twospotted spider mite adult female (E. Beers)
- Mite damage to pear (transpiration burn) (E. Beers)
- damaged pear leaves on a tree
- Mite damage to pear (transpiration burn) (E. Beers)
- Mite damage to pear (transpiration burn) (E. Beers)
- Twospotted spider mite adult females (E. Beers)
- two females on a leaf
- Twospotted spider mite adult females (E. Beers)
- Twospotted spider mite adult females (E. Beers)
- Twospotted spider mite adult female (E. Beers)
- adult female with two large spots on either side of the body
- Twospotted spider mite adult female (E. Beers)
- Twospotted spider mite adult female (E. Beers)
- Twospotted spider mite diapausing female on cherry (E. Beers)
- diapausing female on a leaf
- Twospotted spider mite diapausing female on cherry (E. Beers)
- Twospotted spider mite diapausing female on cherry (E. Beers)
- Twospotted spider mites (E. Beers)
- leaves covered with mites
- Twospotted spider mites (E. Beers)
- Twospotted spider mites (E. Beers)
- Twospotted spider mites (E. Beers)
- cluster of mites on the tip of a leaf
- Twospotted spider mites (E. Beers)
- Twospotted spider mites (E. Beers)
- Twospotted spider mites (E. Beers)
- two leaves with mites
- Twospotted spider mites (E. Beers)
- Twospotted spider mites (E. Beers)
- Twospotted spider mites (E. Beers)
- mite clusters on the tips of grass blades
- Twospotted spider mites (E. Beers)
- Twospotted spider mites (E. Beers)
- Twospotted spider mites on base of peach tree (E. Beers)
- mites web at the base of a tree with brown blades of grass and leaves
- Twospotted spider mites on base of peach tree (E. Beers)
- Twospotted spider mites on base of peach tree (E. Beers)
- Twospotted spider mites on peach twig (E. Beers)
- mites web covering a peach twig
- Twospotted spider mites on peach twig (E. Beers)
- Twospotted spider mites on peach twig (E. Beers)
by Stanley C. Hoyt and Elizabeth H. Beers, originally published 1993
Tetranychus mcdanieli McGregor (Acari: Tetranychidae)
The McDaniel spider mite was first described on raspberry in Michigan in 1930 but has gained pest status only on tree fruits in the Pacific Northwest, Utah and certain areas of California, usually in the drier areas. It has been most studied as a pest of apples in central Washington where it has been a pest since the 1930s. Widespread outbreaks occurred during the late 1950s and early 1960s as a result of severe disturbance of biological control. These outbreaks led to the orignal studies on integrated mite control, which has been successfully implemented in the majority of Washington apple orchards since that time. While McDaniel mite was the primary outbreak species in central Washington during that period, it has become relatively uncommon in recent years.
Although McDaniel spider mite is considerably less polyphagous than twospotted spider mite, its host range is still fairly broad. It attacks most deciduous tree fruits (apple, pear, sweet and sour cherry, prune, peach and apricot), some field and vegetable crops (squash, asparagus, alfalfa, clover), and a number of weeds (mallow, milkweed, knotweed, ragweed, mustard, dock, wild buckwheat, wild lettuce). In a study of numbers and survival of eggs, Red Delicious apple, sweet cherry and apricot were better hosts for McDaniel spider mites than pear, peach and sour cherry.
The egg is spherical and about 1/150 inch (0.13 mm) in diameter. It is translucent when first laid but becomes darker. Just before hatch it assumes a dull ivory color, and the red eyespots of the embryo are visible. McDaniel spider mite eggs cannot be distinguished from twospotted spider mite eggs.
The larva has three pairs of legs and is about the same size as the egg. It has little or no color until it begins feeding when it takes on a greenish tinge from leaf chlorophyll. The quiescent stage is about 1/12 inch (0.20 mm) long. The protonymph is oval and dark green and has four pairs of legs. The female is 1/100 inch (0.25 mm) long, and the males are slightly smaller. The deutonymph also has four pairs of legs and is generally the same color and shape as the preceding stage, only larger. The female, which is about 1/70 inch (0.35mm) long, can readily be distinguished from the male at this stage. The male has characteristic slender, tapered abdomen and is distinctly smaller than the female.
The adult female is about 1/60 inch (0.44 mm) long, whereas the male is only about 1/80 inch (0.29) long. The adult female, like the deutonymphs, can also be distinguished from the male by its shape. The female has a broad oval shape, whereas the male has a slender, more pointed abdomen. The dark spots on the abdomen that characterize this species occur on all stages but are most distinctive in the older stages. The earlier stages may be difficult to distinguish from twospotted spider mite because of the variability in both species. McDaniel spider mite has multiple pairs of spots, some of which always occur in the posterior portion of the abdomen.
Twospotted spider mite, on the other hand, usually has two fairly distinct spots, and the area of pigmentation is confined to the front half of the abdomen. Both species lose their spots during a molt and do not regain them until they begin feeding again. Because of the variability, identification may be difficult. However, slide mounting and examination under high magnification make it possible to distinguish the two species.
The McDaniel spider mite overwinters as an orange-colored diapausing female under bark scales or in litter at the base of the tree. Overwintering mites, which are often in large masses, produce extensive webbing. The mites emerge from their overwintering sites in March or April, depending on the area, but at about the time fruit buds begin to open. They move to the green tissue and begin to feed. Mites may move directly into the tree fruit host or, if available, to nearby weed hosts. As they feed, they lose their orange color and take on the normal greenish tinge and characteristic dorsal spots. After a few days of feeding, egg laying begins.
Eggs are initially laid on the undersides of leaves, but when populations are high both sides of the leaves are colonized. In apple, the mites tend to stay close to the main trunk and scaffold limbs initially so their distribution in the early part of the season covers a cone-shaped area in the center of the tree. Although there is some lateral distribution, McDaniel spider mites do not tend to infest terminal growth because they prefer older foliage.
Eggs are laid either in or beneath the webbing, possibly providing protection from some chemical sprays and predators other than T. occidentalis. Summerform females can lay up to 150 eggs over a 5- to 6-week period. The time required to complete development at very high temperatures can be as little as 6 days, but at typical midsummer field temperatures development requires about 8 to 11 days. There are up to 10 overlapping generations per year in central Washington, depending on the temperatures. In the absence of predators, populations peak in late July to mid-August, then decline. Overwintering forms may be produced as early as May if foliage quality deteriorates, but they are usually produced from mid-July through September. The males die with the onset of cold weather, and the orange-colored females seek sheltered sites to spend the winter.
Spider mites all cause the same type of feeding damage (see damage section under European red mite). In addition, the McDaniel spider mite forms very dense webs on leaves and fruit. Webs on the leaves may prevent good spray penetration, making chemical control more difficult. Mites and webbing in the calyx end of fruit have also been noted as a problem since this species is regulated by quarantine in certain countries.
The basic scheme for monitoring spider mites is the same for all three of the more common species. See the general description under European red mite and the sampling plan for McDaniel and twospotted mites below.
Damage, Biological Control, and Management
see sections under European red mite
Super Simple Spider Mite Control and Prevention
FAQ
Can a plant recover from spider mites?
What is the best treatment for spider mites?
What is a homemade solution for spider mites on plants?
How long does it take to get rid of spider mites on plants?
How do you get rid of spider mites on houseplants?
Spider mites on houseplants can often be washed way. If your plant is of manageable size, take it to your sink or bathtub and use the sprayer attachment to give the underside of the plant a good washing. Don’t be timid. Spray them right off. You can gently rub the leaves while spraying to help knock them loose.
Do spider mites eat leaves?
Spider mites tend to bite a leaf many times in the same area, so there are usually many holes in a cluster close together. Sap is fluid found in a plant’s leaves. It carries food, waste, and other essential nutrients around the plant. It’s also what makes a plant’s leaves firm enough to hold its shape. Spider mites eat plant sap.
How do you kill Spider mites?
Dust the powder on the plant’s leaves, stems, and surrounding soil. You can also make a homemade spider mite killer spray by mixing 4 tablespoons of diatomaceous earth with a gallon of water. Use it to spray the critters. Once the solution dries out, it will dehydrate them to death. 9. Hot Pepper Spray
What do spider mites eat?
Spider mites are tiny, eight-legged pests that feed on the sap of plants. They are related to spiders and are considered to be a type of arachnid. There are many different species of spider mites, but all are known for causing damage to plants by feeding on the sap within the leaves and stems.