Insect Control
Aphids (Coastal Area and Seed Production Areas in the Interior)
The green peach aphid, the potato aphid and the cotton aphid spread leaf roll and other viruses, and can cause physical damage to plants by feeding in large numbers. The green peach aphid is almond-shaped, usually yellow and is primarily found on the lower leaves. The potato aphid is similar in shape and colour, but is larger and is usually found on the upper leaves. The black cotton melon aphid, recently introduced from California, is similar in size to the green peach aphid, but resistant to most insecticides.
In past years, leaf roll outbreaks have been associated with infected seed sources and aphids arriving from overwintered host plants. The planting of certified virus-free seed has lowered the threat of leaf roll in recent years. This is generally true in table grade potatoes, but serious leaf roll problems can still develop rapidly if the cultural and chemical control practices listed below are not followed. In seed potatoes, seasonal aphid control is a requirement to ensure that adequate virus-free quality is maintained.
Cultural Control
The cultural procedures listed will prevent the build-up of leaf roll virus inoculum on farms. These practices will also reduce the threat of other common insect and disease problems.
1. Plant only B.C. certified seed potatoes if possible. Planting uncertified seed can lead to serious leaf roll problems.
2. Practice proper crop rotation and avoid planting potatoes in the same field in successive years.
3. Destroy all culls and volunteers from previous potato plantings.
Biological Control
Naturally occurring predators and parasites of aphids can often play a major role in suppressing aphid populations in table grade potatoes. Since fields must be monitored accurately and routinely to make proper use of these beneficial insects, interested growers are advised to contact a commercial monitoring service for advice.
Chemical Control
See Table 2, Potato Insect Control. For potato seeds, initial protection can be obtained with application of a seed treatment (see Table 4, Potato Seed Piece Treatments). Foliar spraying of seed potatoes for aphids should begin after mid-July. Table potatoes should be sprayed if aphid levels become noticeable. In the Lower Mainland, commercial monitoring services are available for tuber flea beetle and aphid populations. For further information contact the BCAGRI office at Abbotsford.
Colorado Potato Beetle (Interior of B.C.)
Beetles are yellow and black striped. Larvae are reddish orange, with two rows of black spots on each side. Eggs are laid in yellow clusters on the underside of leaves. This pest tends to develop resistance to insecticides. Rotation of products is essential.
Control
Treat when pest reaches economic levels with a product recommended in the Table 2, Potato Insect Control. Young larvae are easier to kill than adults.
Tuber Flea Beetle
Small, black, fast-jumping beetles eat holes in leaves causing a shot-hole appearance. Larvae feed by tunneling just beneath the skin of the tubers. Heavy feeding in a tuber produces a network of fine tunnels that cause cracks and pimples on the surface; which, later, may resemble common scab.
Control efforts should concentrate on achieving complete control of the flea beetles as they first enter the crop in May and June. This will reduce the need to routinely spray for this pest later in the growing season.
Monitoring
Beginning on May 15, sample all emerged fields or volunteers for tuber flea beetles. Fields should be sampled even if only 25% of the crop has emerged. When plants are small, visual observations to detect beetles or damage to the foliage should be made at regular 7-day intervals. Observe 10 samples of 10 consecutive plants each per hectare; i.e. 100 plants.
Treat immediately as outlined below if there is an average of more than one beetle or feeding hole per sample of 10 plants.
Later, when the foliage is about 15 cm high, assess the flea beetle population by sweeping with a 35 cm net at 7-day intervals throughout the growing season. Twenty-five samples of 10 net sweeps each (i.e. 250 sweeps) is adequate for fields of 4 ha (10 acres) or larger, providing the samples are taken around the outside 4 rows as well as diagonally from corner to corner in two directions. Net sweeping is reliable only under conditions of low wind, bright sunlight and temperatures over 21°C. Treat immediately as outlined below if there is an average of more than one beetle per sample of 10 net sweeps.
Beetles migrate from one field to another so net sweeping is more effective if done on an area wide basis.
In the Lower Mainland, commercial monitoring services for tuber flea beetle and aphid populations are available. Late blight monitoring is also a part of the insect monitoring program. Contact the BCAGRI at Abbotsford for further information.
Cultural Control
Follow the cultural control methods described for aphids above.
Flea beetles first invade potato fields along the outer rows. Planting the outer rows of potatoes to parallel all sides of the field will enable more effective edge treatments. The number of outer rows should equal the number of rows covered by a sprayer swath.
Fields must be rotated to avoid subsequent infestations inside the field, leading to many more sprays per crop.
Chemical Control
The proper choice of insecticide is important in controlling the first beetles. In May and June, synthetic pyrethroids such as Pounce or Ripcord should be used. These products are very toxic to flea beetles and last almost twice as long as the other products listed. They also work well in cooler temperatures. It is best to avoid using these insecticides later in the season, if possible, as they have low toxicity to aphids, but are toxic to beneficial insects.
For good control, upper and lower surfaces of leaves must be covered with the insecticide. Use a drop-pendant sprayer and vine-lifters. Apply sprays in 800 to 1000 L/ha (300 to 400 L/acre) of water.
Early Crop – Treat when beetle or damage is observed on the leaves or on June 1 to 7, whichever is first.
Mid and Later Season Crops – Begin treatments when plants are 5 cm high.
See Table 2, Potato Insect Control.
Leafhoppers
Leafhoppers are small, flying insects, gray, green or brown in colour and measure up to 5 mm. They are present in great numbers in grassy and bushy field borders in July and August and invade potato fields. They are sucking insects and some species transmit the diseases Aster Yellows and Witches’ Broom. See “Disease Control”, this section.
Control
See Table 2, Potato Insect Control. Sprays should be applied when potato plants are 10 cm high, if leafhoppers are present.
Where possible, spray areas 9 to 15 m wide surrounding the field; this kills the leafhoppers before they get to the potato field. Leafhoppers move into potato fields when surrounding vegetation begins to dry up.
Loopers, Climbing Cutworms and Other Caterpillars
Loopers, cutworms and other caterpillars are the larval stages of moths and butterflies. Loopers are usually green with thin white stripes along the body. Cutworms and other caterpillars may be green, brown or gray. They vary in size and can measure up to 5 cm long when fully grown. There are one or more generations each season, depending on the species
Chemical Control
When insecticides are used routinely for aphid and flea beetle control, loopers and caterpillars will also be controlled. When monitoring programs reduce spray applications, loopers and caterpillars may reach a damaging level and require specific treatment. For best control, these pests should be sprayed when small. See Table 2, Potato Insect Control.
Spidermites
Spider mites (<1 mm long) cause damage to the leaves during prolonged warm periods, particularly in mid- to late summer. They feed on the lower leaf surface with piercing mouthparts resulting in pale flecking being visible from the top surface. Mites create webbing for protection and dispersal between plants. Heavy infestations can result in leaves drying up and dropping off.
Control
Spider mites build up as the season progresses, therefore, the crop should be checked weekly. If spider mites appear in early summer, or populations escalate, apply a miticide. Two applications 7 to 10 days apart may be needed, depending on level of infestation. See Table 2, Potato Insect Control.
Thrips
Thrips cause damage by feeding with rasping mouthparts on leaf surfaces. Leaves can look silvery, scarred, or bronzed. Black fecal spots are evident in areas where thrips are feeding. Insects are small (<1 mm long), thin, yellow to brown or black, and fast-moving. They can be difficult to find as they are easily disturbed and hide in/under plant parts.
Control
Thrips populations build up as the season progresses. They commonly inhabit headlands, ditches, and flowering crops. thrips are attracted to flowering plants. Once flowers dry down or plants are mowed, thrips move to neighbouring areas, and high thrips populations can occur quickly, therefore, the crop should be checked weekly. Broad spectrum insecticides registered for aphids for other pests will also control thrips.
Wireworms
Wireworms, which are yellowish‑brown, shiny, slender, hard‑bodied worms 3 to 25mm long, are the larval stage of click beetles. In the lower Fraser Valley, two introduced European wireworms have been causing the majority of damage. These European species have what appear to be two dark eyes at the more pointed end of the body. The click beetle stage of the European wireworm is about 1 cm long, and is a fairly uniform dark brown or black colour. Wireworms generally build up to high levels in pasture or wherever there is longstanding grass or sod. When these areas are ploughed, wireworms remain in the soil and will then bore into newly planted seeds or seedlings of many vegetable crops. Wireworms can destroy plants directly, reduce yields, or cause serious cosmetic damage to root crops such as carrots and potatoes.
Heavy infestations occur in fields previously in sod, or surrounded by wooded or grassy areas. Depending on the species, wireworms may live from 3‑6 years in the soil. The European wireworm life cycle begins with overwintered adult click beetles, which emerge from soil in March or April, and lay eggs for up to 3 months. Eggs are deposited in the soil, normally near a preferred host such as sod or cereal crops. Within about 6 weeks, the eggs hatch into small larvae. After 3 or 4 growing seasons, these larvae become pupae and then adults, usually in August, and these adults remain in the soil overwinter and emerge to deposit eggs in the following spring.
Monitoring
Before planting, baits of whole-wheat flour can be used to determine the presence of wireworms. This is done by placing 30 g of flour at a depth of 10cm in the soil using a hand corn planter or a shovel and marking the location of each bait with a stake. To obtain an accurate reading, 30 to 50 baits should be used per hectare. Four days later, dig and examine the baits for wireworms. An average of one or more wireworms per bait can cause severe damage to a crop such as potatoes or corn. In the Fraser Valley, most wireworms are near the soil surface in April and May, and this is the best time to use the baits. After May, wireworms are deeper in the soil, and so baits will be less effective and you might think the problem is not as bad as it actually is. In the Interior, wireworms may descend to a depth of 60cm in the fall and may not return to near the surface until the soil warms up sometime in May. Attempts to determine the presence of wireworms in these areas before this time may also indicate a lower population than actually exists. Baiting works best when fields have been fallowed in the fall, have low green manure content and no weeds. Baiting results will be inconsistent in recently ploughed fields, or in fields with competing crops or weeds.
Pheromone traps have been developed for the two European species, and these are available from Contech Inc. These traps attract the male click beetles, and can be used to determine what species are in a field, and whether the field is at risk of wireworm damage. For further information contact the Abbotsford BCAGRI office.
Control
Chemical: When it is known that wireworms are in a particular field, insecticides should be applied as recommended for wireworm control on that crop. Titan ST (clothianidin) is registered as a seed treatment for damage suppression of wireworms. Growers should be aware that it will cause wireworms to stop feeding only temporarily, and that they will eventually recover. See Table 4, Potato Seed Piece Treatments for label information.
To maximize the effectiveness of the granular formulation:
Under soil conditions where a minimum of crop residue is present, wireworms will be obliged to feed on the treated potato seed pieces and will be more effectively controlled. Since wireworm problems are increasing each year, use every opportunity available to reduce their numbers. See “Wireworms”, Pest Management section of this guide for more information.
