Aphids, Mites and Thrips on Transplants

Many vegetable crops are grown from transplants in Connecticut. Transplants enable growers to get the most out of a short growing season and can assist in getting a harvestable crop as soon as possible. Regular scouting is necessary when starting seedlings in greenhouses as unchecked pest pressure can spiral, stressing young plants, creating wounds or other environmental conditions for disease to take hold, and diminishing the overall health of transplants.

Aphids

Several species of aphids can occur on vegetable transplants, but the most common are green peach, melon, foxglove, and potato. Aphids feed by inserting their piercing, sucking mouthparts into plant tissue and removing fluids. In greenhouses, aphids are usually females. Each female can produce 50 or more nymphs. Nymphs mature to adulthood and begin reproducing in as little as 7-10 days. Adult aphids are usually wingless, but some will produce wings when populations reach outbreak levels. Large numbers of aphids will stunt and deform plants. Physically removing wingless aphids by shaking the plant or spraying with water can help since they will have a hard time climbing back up onto their host plant.

In addition to feeding damage, aphids are also problematic because they can transmit certain viruses. Aphids also produce a sticky digestive by-product called honeydew that covers leaves and provides a food source for a superficial black fungus known as "sooty mold." Signs of aphid activity include shed white skins (sometimes mistaken for white flies), shiny honeydew, curled new leaves, distorted growth, and the presence of ants. Examine plant foliage, stems and new growth – especially in key plants such as pepper, eggplant, brassica crops, and leafy greens – to detect potential aphid infestation as early as possible.

Mites

There are three main types of mites that threaten transplants in the greenhouse: broad mites, spider mites, and cyclamen mites. Because they are small and the undersides of leaves, on new growth, or within tender buds or flowers, they can be challenging to detect. Look for inward curling leaves, puckering and crinkling. You can also use a hand lens or microscope to look within buds for mites and their eggs. Spider mites will create webbing and discolored foliage like light flecking or speckling when high populations have developed.

Mites can be controlled chemically or biologically. One of the most common strategies for combatting problematic mites in the greenhouse is through predatory mites.

Thrips

Thrips easily go undetected until considerable damage is done since they are small, feed in plant buds, and multiply rapidly. Feeding marks appear as white streaks on leaves and infested new plant growth may curl under or cause deformed leaves. Look for distorted young leaves and silvery flecked scars as signs of feeding damage. Female thrips insert several hundred eggs into plant tissue, and the tiny, yellowish larvae will feed on plant fluids as they mature. Warmer temperatures cause development and maturity to quicken. Eggplant, tomato, pepper and leafy greens are all prone to thrips infestations.

Yellow sticky cards should be placed just above the crop canopy, near doors and vents, and over thrips-sensitive cultivars to monitor their movement. It’s important to detect thrips as early as possible, because damage will only continue once seedlings are transplanted in the field.

Please see insecticides labeled for insects and mites on vegetable transplant. You can find a table listing such insecticides on the New England Vegetable Management Guide website. 

Brassica Flea Beetles

Brassica flea beetles will soon be active. Adult beetles overwinter outside cropped fields, in the soil surface and decaying plant residue of shrubby or woody borders. They search out host crops from early May into June and feed on leaves and stems, leaving small round pits and holes. Eggs are laid in soil near the plant. Tiny white larvae feed on root hairs and pupate underground. New adults emerge from mid-July through early August and feed throughout August.

Crops with more waxy leaves (Brassicas such as cabbage, broccoli, and kale) are less attractive and feeding is more restricted to leaf margins, especially as crop matures. Crops with glossy leaves (e.g. bok choy, Napa cabbage, or mustard greens) are highly attractive. The whole leaf is susceptible to damage, making the crop susceptible until harvest. Be sure to protect direct-seeded crops and young transplants with a row cover or chemical control. Non-waxy brassica crops can be planted alongside waxy brassicas and sprayed regularly to function as a trap crop and reduce sprays to less preferred crops. A working threshold of 1 beetle per plant or >10% average leaf damage on 50% of the plants has proved effective in leafy greens and early stages of heading brassicas. Repeated applications may be needed if pressure is high. A list of labeled products can be found in the New England Vegetable Management Guide. Spinosad (e.g. Entrust) is an effective OMRI-listed material. Kaolin clay (e.g. Surround) will protect young transplants but needs to be frequently reapplied to cover new growth and will wash off in rain.

The emergence of asparagus every spring coincides with the renewed presence of asparagus beetles. There are two beetle pests of asparagus, the common asparagus beetle (CAB) and the spotted asparagus beetle (SAB). They overwinter as adults in protected areas along fields, feed and lay eggs in the crop, pupate in the soil, and have two or sometimes three generations per year. Depending on the size of the population and intensity of pest pressure, common asparagus beetle larvae may cause severe defoliation of ferns and lead to the decline of the planting. On the other hand, spotted asparagus beetle larvae feed only on berries. This can weaken the plant in the fall and lead to a lower yield the following year.

During harvest, scout for adults and eggs on sunny afternoons. Treat spears if >10% of the plants are infested with beetles or 1-2% have eggs or damage. If possible, spot spray to help conserve natural enemies. During harvest, snap or cut spears close to the soil surface daily. A tiny metallic green wasp, Tetrastichus asparagi, parasitizes asparagus beetle eggs. They have been known to provide very effective control, parasitizing up to 70% of the eggs. Lady beetle larvae and other predators may also be active; they will consume both eggs and larvae as well as asparagus aphids. Entrust, PyGanic, Suffoil, or Radiant can be sprayed. Surround WP may also work as a repellent. For more information on insecticide applications for asparagus beetles, please refer to the NE Vegetable Management Guide.

You may be noticing that some recent transplants are showing purple leaves and dark foliage. In many cases, this is a temporary phosphorus deficiency caused by cold soils, not a true lack of phosphorus in the soil. Cold conditions slow root growth and limit phosphorus uptake, especially in young plants.

Typical symptoms include purpling or reddish-purple color, often first seen on older leaves, along with slow growth or stunting. These symptoms are usually most noticeable in cold, wet, or compacted soils.

Do not assume that every purple seedling needs more fertilizer. In many cases, the best response is to let soils warm and watch how new growth develops. It is also worth checking for wet areas, soil compaction, and poor root development. If symptoms continue after warmer weather arrives, confirm the problem with a soil or media test before making fertilizer decisions.

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