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Conrad Bérubé island crop management email: uc779(at)freenet.victoria.bc.ca |
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Conrad Bérubé island crop management email: uc779(at)freenet.victoria.bc.ca |
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Tuber flea beetles and aphids are the key
pests around which IPM is structured. Potato flea beetle,
Epitrix tuberis, causes subepidermal burrowing that causes
cosmetically unacceptable damage (1-2 beetles in one hundred
plants at beginning of season can result in late season damage).
These Chrysomelids are easily recognized by their expanded hind
femurs. The 8-10 holes per leaf that adults cause are relatively
insignificant, damage is primarily caused by larvae. Adults and
pupae peaks occur in middle of June, beginning of August and end
of September. Tuber flea beetles seem to come in from one
direction predominantly. The adults can overwinter in brush and
soil of old potato fields. Mustard and lambsquarter may harbor
the flea beetles. If plants are less than a foot tall then they
need to be examined visually. On windy days the beetles will not
be as active on upper sides of the leaves. Time of day is not so
important for sampling accuracy. Generally a sweep catches about
1% of beetles. Synthetic pyrethroids are the weapon of choice for
the beetles. Outside edge or localized sprays are generally
effective for control of flea beetles.
Flooding of fields can kill many of the overwinterers. Beetles may survive on high ground,m pastures, or headlands. When rouging of volunteers with beetles occurs the beetles may move into new crop.
These volunteers may also serve as potential sources of inoculum of pathogens of blight and leaf-roll virus.
The larvae are evident from late May throughout growing season. Beetles can increase two hundred fold each generation. Peaks occur in mid-July, early August and late September. Damage in early season is often small channels that can be peeled off. Later in the season the suberization forces the larvae to bore through the skin and into spud causing cosmetic damage and down-grading. IPM focuses on controlling the first generation of beetles so that only mop-up and spot-treating is necessary later in the season. Field rotation is first line of defense to reduce flea beetle population (otherwise you may get beetle populations building up in center of field). Monitor only gives three days of protection after spraying. Ideally its nice to have growers break field into sections (that are larger on edges that historically have had beetles there before or have prevailing winds). If you can get them to plant outside first the outer edges will plant from inside-out because it gives them more turning room). The impetus in IPM is to do timely (early-season) with something harsh (Cymbush, Decis) which will give long-term protection at a time when there are not a lot of beneficials in the field. (Cymbush and other synthetic pyrethroids are toxic to fish but less so to humans and other mammalian species). Monitor, Sevin, Thiodan and other OP and Carbamates offer less residual activity than the synthetic pyrethroids.
The peak beetle population tends to be several rows in from the edges (so when they're in the borders, sample towards the center until they're no longer detected). About five seconds per plant is adequate for an experienced scout to detect all the beetles on one plant. Wind and fatigue can impact the accuracy of sampling for beetle (accuracy is better in the morning when it's calm and scouts are fresh). Beetles tend to move under the leaves at night or in adverse environmental conditions. Visual plants). Sweeping is only about 3-4% accurate (but more convenient).
15-20 paces between sampling plots: on plants less than a foot tall do a visual inspection of 10 plants in a row or, if sampling across rows, choose two plants from each of five rows.
If plants are greater than a foot tall, make ten consecutive full-circle sweeps (such that each sweep shares a single tangential point with the previous circle-- the intent being to sweep one hundred plants) and count the resulting beetles-- THE THRESHOLD IS ONE BEETLE PER ONE HUNDRED PLANTS. If beetles are found to be above threshold take sufficient samples to delimit the area of infestation (to determine whether border spray will be sufficient or if the whole field should be treated.
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