|
September 2002, No. 4
AUTUMN
WEED CONTROL LEADS TO A FINER SPRING
Fall is a fantastic time of the year (if one can find the time)
to treat for broadleaf weeds. With the spring we endured this
year, there are many broadleaves that still need to be eradicated.
Several factors of this peculiar spring made it difficult to find
a window to have a successful herbicide application on many of
the broadleaves. Those who treated early this year found unsatisfactory
control due to the shift from warm to cool temperatures. As the
temperatures leveled out, seasonal rains prevented successful
attempts for broadleaf weed control. For those who waited for
the rains to cease, the plunge into summer replaced the hope of
treating for broadleaves with the hope of rainfall and mild temperatures.
As temperatures become more moderate this time of year, many
of the broadleaf weeds that are problems in the spring can be
treated now. Recall on every broadleaf herbicide label is statement
"treat when the weeds are actively growing". This spring,
weeds vacillated between active and inactive growth because of
the shifting environmental conditions. At present, many weeds
are beginning to become active again through their natural growth
cycle.
WHEN ARE THE WEEDS ACTIVELY GROWING?
Weeds, like turfgrasses have one of two different growth cycles.
The difference between cycles among plants is due to the adaptation
to certain climatic conditions. The two predominate conditions
that dictate plant survival (or adaptation) are temperature and
moisture.
The first cycle is described as cool-season. A cool season weed
or plant is most active at temperatures between 60 to 75°F
and in our region has two periods of active optimum growth (see
Table 1). Most of the desirable turfgrass species that we manage
fall into this category. Kentucky bluegrass, perennial ryegrass,
creeping bentgrass and the fescues are all cool season grasses.
The majority of broadleaf weeds that we encounter are also cool
season plants (see Table 2). Many of these plants are starting
their second period of active growth right now. This makes it
an ideal time to effectively and efficiently control these weeds.
The other cycle is described as a warm season cycle. Plants in
this category have only one season of active growth when temperatures
range between 80 to 95°F (see Table 1). Broadleaf weeds that
fall into this category are not as numerous as the weeds in the
cool season category. Warm season broadleaf weeds are more effectively
controlled with a midsummer to early autumn herbicide application
when the weeds are still active. However, if temperatures continue
to stay mild some control may be achieved on these weeds this
fall.
Table 1.
Table 2.
|
Cool Season Broadleaf Weeds
|
Warm Season Broadleaf Weeds
|
| White clover (Trifolium repens) |
Common purslane ( Portulacca oleracea) |
| Common chickweed (Stellaria media) |
Yellow woodsorrel (Oxalis stricta) |
| Common violets (Viola spp.) |
Spotted spurge (Euphorbia maculata) |
| Buckhorn plantain (Plantago lanceolata) |
Black medic (Medicago lupulina) |
| Henbit (Lamium amplexicaule) |
Cool Season/
Warm Season
|
| Ground ivy (Glechoma hereaceae) |
| Mouseear chickweed (Cerastium vulgatum) |
| Broadleaf plantain (Plantago major) |
| Dandelion (Taraxacum officinale) |
| Red sorrel (Rumex acestosella) |
| Curly dock (Rumex crispus) |
A NEW PRODUCT TO TRY
PBI/Gordon released a new herbicide containing the new chemistry
carfentrazone-ethyl in the fall of 2001. The product is called
Speed Zone™. Carfentrazone is classified as a protox inhibitor.
|
A PROTOX INHIBITOR?
This chemistry inhibits a key enzyme in chlorophyll
production causing disruption to plant membranes. Carfentrazone
is in the triazolinone family that is believed to disrupt
cell membranes similar to the diphenyl ethers by inhibiting
the enzyme protoporphyrinogen oxidase (the PROTOX enzyme),
thus they are called PPO or protox-inhibiting. PPO is the
enzyme responsible for the last step in the pophyrin pathway
that produces chlorophyll. The production of protoporphyrin
requires light. Symptoms from foliar applications occur
most rapidly under bright, sunny conditions. PPO inhibitors
cause an accumulation of large amounts of the phytotoxic
molecule protoporphyrin IX, which in turn can react with
oxygen and light leading to the formation of singlet oxygen.
Singlet oxygen then causes rapid lipid peroxidation, membrane
destruction, and cell desiccation and death. Injury symptoms
can occur within 1 to 2 hours after application, appearing
first as water-soaked foliage, which is followed by necrosis
of the tissue wherever the spray contacts the foliage. These
herbicides are often referred to as photobleaching herbicides
because a primary symptom is bleaching of plant foliage.
Protox or PPO-inhibitor chemistry has been around since
the 1970's. There is a renewed interest in this type of
chemistry at present. Many of the PPO inhibitors have:
· Low volatility
· Low toxicity to mammals
· Favorable environmental impact profiles
· Degraded by sunshine and microbial action
· Short half-lives in soil (4 to 6 weeks)
One PPO-inhibitor that has been used for years is oxadiazon
(a.i. in Ronstar®).
|
SpeedZone™ also contains the active ingredients; 2,4-D, mecoprop
and dicamba. This product claims several features not common to
typical broadleaf herbicides. The first is it's quick action.
Some plants are reported to show sign of injury within several
hours (clover, plantain, ground ivy and spurge). This can be helpful
when treating a client's lawn and weed damage can be seen the
same day.
Another feature that may allow the turf professional greater
flexibility is the extended application window in spring and fall.
SpeedZone™ is reported to have good activity even in cooler weather.
This can extend the opportunity to treat for broadleaf weeds later
in the fall and earlier in the spring. SpeedZone™ is rain fast
in as little as three hours, and the area can be reseeded within
two weeks after application.
FREE UP SOME TIME NEXT SPRING
BY TREATING THIS AUTUMN…………
Take advantage of the cool season growth cycles of many broadleaf
weeds. As the desirable turfgrasses begin their active growth
with moderate temperatures, clean-up any leftover weeds from spring.
The turfgrass will fill the void before winter sets and there
will be one less task to tackle in spring.
Remember these things when controlling broadleaf weeds this
fall:
1. Proper identification of the trouble weed is the key component
in any eradication program.
2. Treat when the weeds are actively growing. If the area is un-irrigated,
wait until after a rain to make an application. If a weed is suffering
from drought stress, any herbicide will be less effective.
3. Always read, understand and follow any pesticide label prior
to making an application.
Luke Cella, CGCS
Editor Turfgrass Tips
Please note: Product names are not intended as endorsement of
the product of a specific manufacturer, nor is there any implication
that other formulations containing the same active chemical are
not equally as effective. Product names are included solely to
aid readers in locating and identifying the herbicides contained
in them.
|
