A BUNCH OF SUCKERS
(Art Agnello ama4@nysaes.cornell.edu,
Entomology, Geneva)
Comstock Mealybug
The first Comstock
mealybug adult males of the season showed up last Friday (6/25) in
our Wayne Co. pheromone traps, so it shouldn't be long before we start
seeing some adult females in pear foliage, followed by their invasive
crawler offspring. For those with a history of infestations of this pest
in their pears, the crawlers are the most susceptible stage for chemical
control, which we expect sometime during the 2nd to 3rd week of July in
the Hudson Valley, and shortly thereafter in western N.Y. The following
information is taken from the Comstock Mealybug IPM Fact Sheet, No. 22:
There are two generations of Comstock mealybug in New York, each
taking 60 to 90 days to complete, depending on seasonal temperatures.
The egg is generally thought to be the primary overwintering stage, but
some nymphs and adult females from the second (summer) generation may
also overwinter, with eggs being laid in the spring rather than the previous
fall. Adult females and males emerge at the same time, from late June
to mid-July for the first (overwintering) generation, and late August
to mid-September for the second (summer) generation. Adult females are
present for a total of 4—6 weeks, and oviposit for about one week
after mating. Males survive for only a few days after emerging.
Eggs of Comstock mealybug
The elongate, orange-yellow eggs are laid in jumbled masses along
with waxy filamentous secretions in protected places such as under bark
crevices, near pruning cuts, and occasionally in the calyx of fruit. The
summer-generation eggs are laid from mid-June through late July, and the
overwintering eggs from mid-August into October. The early larval instars
of the CMB are similar to adult females (wingless and elongate-oval in
shape, with a many-segmented body) except that they are smaller, more
oval-shaped, lack the long body filaments, and are orange-yellowish because
they have less wax covering. Later instars are similar in appearance,
but become progressively browner and redder.
Comstock mealybug crawler on bark
The overwintered eggs hatch from mid-April through May and the nymphs
(crawlers) migrate from the oviposition sites to their feeding sites on
terminal growth and leaf undersides of trees and shrubs. This hatch is
completed by the petal fall stage of pears. Nymphs that hatch from these
overwintered eggs are active from roughly early May to early July. As
the nymphs approach the adult stage, they tend to congregate on older
branches at a pruning scar, a node, or at a branch base, as well as inside
the calyx of pears. Second- (summer) generation nymphs are present from
about mid-July to mid-September.
Adult Comstock mealybug females in pear calyx
The Comstock mealybug poses two major concerns for the pear processing
industry of New York: First, the emergence of crawlers and adult females
from the calyx of pears at the packinghouse creates a nuisance to workers.
Second, pears to be made into puree typically are not peeled or cored
by processors who buy New York fruit, so infestations can potentially
result in unacceptable contamination of the product.
Another problem, of concern to apple growers in the 1930s and 1940s,
and again in the Hudson and Champlain Valleys in the early 1980s, is that
the honeydew secreted by the crawlers is a substrate for sooty molds growing
on the fruit surface. This problem also occurs on peaches. These molds
result in a downgrading of the fruit, and are therefore an additional
cause of economic loss.
To date, the Comstock mealybug has been a problem to growers of processing
pears because of the contamination and aesthetic reasons noted. An infestation
generally requires one or more insecticide sprays during the growing season,
directed against the migrating crawlers. Examine the terminal growth for
crawler activity periodically throughout the summer. Crawler and adult
female activity can be monitored best by wrapping white, double-sided
carpet tape around low scaffold branches and inspecting for crawlers that
have been caught on the tape. They can be recognized with a hand lens
or, with some experience, by the unaided eye.
Tape trap for monitoring comstock mealybug crawlers
Cjomstock mealybug nymphs stuck on tape trap
When we detect crawlers in some problem blocks we are monitoring,
we'll advise an application of a material such as Penncap-M, Provado,
Diazinon, Lannate, or (on apples only) Lorsban to control this insect.
Woolly Apple Aphid
We have already begun noticing infestations of this nuisance pest
in eastern N.Y. orchards. The woolly apple aphid (WAA), Eriosoma lanigerum,
colonizes both aboveground parts of the apple tree and the roots, and
commonly overwinters on the roots. In the spring, nymphs crawl up on apple
trees from the roots to initiate aerial colonies.
Colony of woolly apple aphid nymphs on bark
Most nymphs are born alive to unmated females on apple trees during the
summer. Colonies initially build up on the inside of the canopy on sites
such as wounds or pruning scars and later become numerous in the outer
portion of the tree canopy, usually during late July to early August.
Their (somewhat limited) presence now can serve as an indication of potential
trouble spots later on.
Aerial colony of wingless adult female woolly apple aphids
Aerial colonies occur most frequently on succulent tissue such as
the current season's growth, water sprouts, unhealed pruning wounds, or
cankers. Heavy infestations cause honeydew and sooty mold on the fruit
and galls on the plant parts. Severe root infestations can stunt or kill
young trees but usually do not damage mature trees. Large numbers of colonies
on trees may leave sooty mold on the fruit, which annoys pickers because
red sticky residues from crushed WAA colonies may accumulate on their
hands and clothing.
Water sprouts, pruning wounds, and scars on the inside of the tree
canopy should be examined for WAA nymphs. Starting sometime in early July,
new growth around the outside of the canopy should be examined for WAA
colonies. No economic threshold has been determined for treatment of WAA.
Aphelinus mali, an encyrtid wasp that parasitizes woolly apple
aphids
Aphelinus mali, a tiny wasp, frequently parasitizes WAA but is
very susceptible to insecticides and thus does not provide adequate control
in regularly sprayed commercial orchards. Different rootstocks vary in
their susceptibility to WAA. Resistant rootstocks such as MM.106, MM.111,
and Robusta are the only means of controlling underground infestations
of WAA on apple roots. WAA is difficult to control with insecticides because
of its waxy outer covering and tendency to form dense colonies that are
impenetrable to sprays. WAA is resistant to the commonly used organophosphates,
but other insecticides that are effective include Lorsban, Thiodan, and
Penncap-M.
Potato Leafhopper
This insect is generally a more serious problem in the Hudson Valley
than in western N.Y. or the Champlain Valley; however, the recent weather
fronts have resulted in a sprinkling of reports in areas that are not
normally affected, so it doesn't hurt to tour observantly through a few
orchards now. PLH does not overwinter in the northeast but instead migrates
on thermals (warm air masses) from the south. Because PLH come in constantly
during the season, there are no distinct broods or generations and the
pest may be present continuously in orchards from June through harvest.
PLH feeds on tender young terminal leaves. Initially, injured leaves
turn yellow around the edges, then become chlorotic and deformed (cupping
upward) and later turn brown or scorched. Damage is caused by a toxin
injected by PLH while feeding. PLH also occasionally causes symptoms similar
to the effects of growth regulators, such as excessive branching preceding
or beyond the point of extensive feeding. PLH damage is often mistaken
for injury caused by herbicides, nutrient deficiency, or overfertilization.
PLH injury may not be serious on mature trees but can severely stunt the
growth of young trees.
Nymphs and adults should be counted on 50—100 randomly selected
terminal leaves in an orchard. Older trees should be sampled approximately
every three weeks during the summer. Young trees should be sampled weekly
through July. PLH nymphs are often described as moving sideways like crabs,
whereas WALH generally move forward and back. No formal studies have been
conducted in N.Y. to determine the economic injury level for PLH on apples,
so we suggest a tentative threshold of an average of one PLH (nymph or
adult) per leaf. Little is known about the natural enemies of PLH, but
it is assumed that they cannot effectively prevent damage by this pest
in commercial New York orchards.
Populations of all leafhopper species in New York are best controlled
with materials such as Provado, Sevin, Thiodan, Carzol, Lannate, or Vydate.
However, many of these pesticides, primarily the latter three, are toxic
to beneficial mites, so make your treatment decision with these factors
in mind.
BEETLES AND BORERS
Japanese Beetle
This perennial pest overwinters as a partially grown grub in the
soil below the frost line. In the spring the grub resumes feeding, primarily
on the roots of grasses, and then pupates near the soil surface. Mike
Villani indicates that the overwintered grub population this season is
larger than last year's (although not as large as in 1995), and adults
have already been seen flying after emergence from upstate N.Y. lawns
as of last week, which is pretty much right on schedule. The adults fly
to any of 300 species of trees and shrubs to feed; upon emergence, they
usually feed on the foliage and flowers of low-growing plants such as
roses, grapes, and shrubs, and later on tree foliage. On tree leaves,
beetles devour the tissue between the veins, leaving a lacelike skeleton.
Severely injured leaves turn brown and often drop. Adults are most active
during the warmest parts of the day and prefer to feed on plants that
are fully exposed to the sun.Although damage to peaches is most commonly
noted in our area, the fruits of apple, cherry, peach and plum trees may
also be attacked. Fruits that mature before the beetles are abundant,
such as cherries, may escape injury. Ripening or diseased fruit is particularly
attractive to the beetles. Pheromone traps are available and can be hung
in the orchard in early July to detect the beetles' presence; these products
are generally not effective at trapping out the beetles. Fruit and foliage
may be protected from damage by spraying an insecticide such as Sevin
or Penncap-M when the first beetles appear.
Dogwood Borer
Dogwood borer moths were flying last week, so they should be laying
eggs in susceptible apple orchards soon (those with succulent burrknot
tissue or suckers). The larva of this clearwing moth feeds on apple trees,
primarily on burrknot tissue on clonal rootstocks. Dilute trunk applications
of an insecticide with good residual activity can provide control of established
infestations. At this point in the season, a spray of Lorsban 50WP or
Thiodan 50WP would be the most effective materials if applied in July
and August; refer to p. 72 in the Recommends for specific rates and dates.
End of this issue: Scaffolds 1999 Index
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