VegNet Vol. 13,
No. 14.
On the WEB at: http://vegnet.osu.edu
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fax, Call 614-292-3857
In This Issue
1. Tomato Insects to be Looking For
2. Crop Reports
3. Are Phosphates The Same as Phosphites?
4. Pumpkin Field Day
Tomato
Insects to be Looking For
Adapted from: Plant & Pest Advisory, Vegetable Crops Edition,
August 2, 2006, by Gerald M. Ghidiu, Ph.D.,
Specialist in Vegetable Entomology, Rutgers Cooperative Research &
Extension at the New Jersey Agricultural Experiment Station
Brown
stinkbugs. This is the time of year when adults are present and moving around
in search of food and egg laying sites. In NJ, feeding has been very low in
field tomatoes, but much higher in high tunnels. Tomatoes are a favored host, especially
if dry weather reduces the availability of native host plants. Now is the time
to pay attention to fruit in the field for signs of feeding. Stinkbug feeding
on tomatoes first appears as a diffuse whitish blotch on green fruit. The spot
changes to bright yellow as the fruit matures. If this feeding is on the
increase in the field or in harvested fruit, consider treating to suppress the
population.
Thrips. These
insects may often be detected by tapping fresh flower clusters over an index
card. If fields are scouted regularly and an upsurge in thrips
numbers occurs in flower clusters, consider treating to minimize subsequent
fruit injury. Later in the
life of the crop, observe
fruit for the presence of gold colored flecks on ripening fruit. These flecks
are from thrips feeding and often form trails or
patches on the fruit surface. If this injury is increasing, consider treating
for thrips. Foliar feeding may occur under heavy thrips pressure. This feeding appears as small necrotic
patches on leaves with small black dots (droppings) in or near the patches. The
tiny, yellow thrips should be easily observed on
leaves if the population is this heavy.
Check fields for aphids
and two-spotted spider mites (TSSM).
Look at 2 complete leaves each on 5 consecutive plants in 10 random locations.
Note the presence of aphid colonies on the undersides of the leaves, as well as
the presence of TSSM. Increasing aphid populations are often detected by the
presence of their cast skins, which adhere to the sticky droppings they
produce. If colonies are increasing over several scouting visits, especially if
aphid droppings are accumulating on fruit, consider an insecticide to reduce
the population. TSSM feeding results in a whitish pin spot,
or stipple, on the upper surface of the leaflet. The mites will be on
the underside of the leaf until colonies become large. At this point, they will
make webs and travel between leaves. Note the number and location of sites with
TSSM. Consider spot treating to prevent further spread into the field. When applying fungicides to limit foliar disease, remember to
include a copper product in the rotation if a bacterial infection is suspected.
Symptoms include necrotic spots or leaf margins (common to bacterial speck,
spot and canker), as well as stem lesions (canker), dark fruit blisters
(speck), dark scabby fruit lesions (spot), and fruit blisters with light halos
(canker). Avoid fields when foliage is wet. Always work from the youngest planting
to the oldest to avoid introducing bacterial pathogens to the younger plants.
Crop
Reports by Hal Kneen and Bob Precheur
Insect report - Both European Corn
borer (12 moths) and Corn earworm (18 moths) were caught this past week
July 26-
Sweet corn harvest includes Incredible, Silver King and several
bicolor varieties. If sprays applied very little worm damage, no sprays a worm
or two in each ear.
Tomatoes are still being shipped into the market, however market
price is declining as homegrown and northern suppliers are now coming into the
market. Canning tomatoes being sold in the field, you pick. Cantaloupes are
being harvested and small amounts of watermelon. Should have
more melons next week.
Need a slow soaking rain for sweet corn growers,
however tomato and melon growers are happy with lack of rainfall but would like
temperatures to moderate into the low 80's during the day.
Harvest continues for most vegetables. Tomatoes and melons started
coming in the last week or more. Sweet corn harvest continues and quality is
good. The recent heat spell is starting to bunch some different maturities
closer together than was the case earlier in the season. Interestingly, some
varieties with the same maturity planted in very late April were harvested
after the same varieties planted in the first week in May.
The usual diseases, as mentioned in previous newsletters, are
still around but protective control measures have been started to keep these
problems under control.
In pumpkins, we are noticing more virus diseases compared to the
last two years.
Are Phosphates
The Same as Phosphites?
By Dr. Steve Reiners,
There has been some confusion
lately over terms used for fertilizers and chemicals containing
phosphorus. Growers have been using
phosphate fertilizers for generations and are familiar with formulations like
super phosphate, triple super phosphate and diammonium
phosphate. All of these materials
provide phosphate derived from phosphoric acid (H3PO4). The phosphate that plants use is in the form
HPO4 and H2PO4, which is quickly converted in
soil from phosphoric acid fertilizers.
Recently, new terms are being used including phosphorous acid (not
phosphoric acid), phosphite (not phosphate), and phosphonite. Unlike
the fertilizer phosphate that contains four oxygen atoms, phosphoric acid and
the related compounds contain only three oxygen atoms. That difference of one atom is very important
and growers need to be aware of that as they develop their fertility and
disease management programs.
Phosphorous acid compounds
(we’ll include phosphite and phosphonite
in this group) play an important role in agriculture as they are the active
ingredient in materials like ProPhyt and Phostrol. These
pesticides are useful in combating diseases like Phytophthora
rot on tomato, pepper, and vine crops.
The problem is some of these compounds are labeled as pesticides, which
required the manufacturer/distributor to spend the time and money to register
the compound. Others are advertised as
fertilizers, which of course bypasses the registration process. These phosphorous acid compounds, although
active against some fungal diseases, do not provide any phosphorus nutrition to
the plant. Plants can absorb these
compounds through roots and leaves and once in the plant, the phosphorous acids
compounds are very stable. Because the
compounds lack one oxygen atom compared to the traditional phosphate molecule,
plants are incapable of using the phosphorus acid as a nutrient source. The phosphorous acid compounds can break down
in the soil to available forms of P, but this process is very slow and will not
provide adequate P nutrition. Studies
have shown that applications of phosphorus acid compounds to plants grown on
soils with moderate to low levels of available P can actually induce a P
deficiency.
The bottom line is that
phosphates are what’s needed for fertilizer but will have no effect on plant
diseases like Phytophthora. Phosphites are
useful in managing diseases but will not provide plants with the phosphate they
need. Knowing the difference can save
you money.
Pumpkin field day -
Western Agricultural Research Station,
7639
(937) 462-8016
Topics: liquid fertilizers, mouse repellent trial, cover crop
demo, Microdochium or white speck evaluation, cultivar
trial, and fungicide efficacy trial.
Both CCA and ODA credits have been applied for, but probably not
more than 1.5 credits for CCA and 1 for ODA.
For more information and complete details Contact:
Jim Jasinski, OSU Extension, Integrated
email: jasinski.4@osu.edu