Herbicide Resistant Pigweed 4: Management in Organic Systems
- [Narrator] Palmer Amaranth and Waterhemp are two problem weeds that pose a growing agronomic challenge in Pennsylvania, as well as many other states throughout the US.
These fast spreading drought resistant weeds are present in at least 17 Pennsylvania counties and are continuing to spread to new fields.
Suppression of these weeds requires diligent scouting, prevention, and diversified management practices.
This Learn Now video will outline the best management practices for herbicide resistant Palmer and waterhemp for organic cropping systems.
The reason these weeds are a rising concern is that their resistance to common types of herbicides has caused them to spread rapidly through conventionally managed operations.
And they're certainly able to spread to organic fields.
There are several characteristics that make them especially difficult to control.
First, they germinate throughout the season.
Secondly, they grow very quickly, up to one to two inches per day.
And each plant produces up to a million seeds.
So they can form a severe infestation fairly quickly.
They're also fairly drought tolerant.
So again, careful and diversified management and scouting are important to prevent these weeds and control infestations.
The first best management practice for organic systems is to monitor seeds purchased to make sure any seeds entering the farm are certified as clean.
Pennsylvania State seed laws are in place to prevent the contamination of crop seed.
Be cautious when bringing in specialty seed mixes such as wild life feed, and native seed mixes as these can be potential carriers of pigweed seeds, as well.
For operations using or producing manure avoid spreading manure sourced from livestock that may have been in contact with Palmer Amaranth or waterhemp seeds.
Pigweed seeds can survive the digestion by livestock and end up in manure.
When the manure is spread on the field the seeds can germinate.
When possible, source manure from operations where there is no known Palmer or waterhemp presence.
Number two, plan crop rotations in a way that helps the crop be competitive against weeds and that allows effective weed management practices.
In fields with known Palmer or waterhemp populations rotations should include early season crops.
This is because the crops can develop canopies and healthy root systems before pigweeds emerge in the spring, and are harvested before mature pigweed plants produce seeds in the late summer to early fall.
Consider winter cereals, cover crops, and perennial hay crops that can be mowed.
For farms that wish to reduce tillage or no-till cover crops can be managed so as to be weed suppressive.
Cover crops that are planted in the fall and terminated in late spring by a roller crimper have been shown to reduce weed emergence in growth and can be integrated as part of a weed control gene.
This practice can be used to help suppress Palmer and waterhemp.
Since Penn State has specific management recommendations in order to facilitate effective cover crop weed suppression, contact your county extension agent or weed science specialist for more information on how to manage cover crops for weed control.
Number three, competitive healthy crops can help control your Palmer and waterhemp by outcompeting the weeds for resources.
Aside from that, healthy fast growing crops are also better able to perform, even if weeds are in the field.
In fact, crop competition is a really important component of cultural weed control.
Some things you can do to support competitive crops are to provide optimal soil fertility, plant into weed-free soil, plant crop varieties that are quick to establish and develop canopies quickly.
Depending on the crop, you may also be able to decrease row spacing.
Number four, the tillage practices that are used in a field containing Palmer or waterhemp can have a big impact on the ability to manage these weeds.
Knowing the biology of these weeds is important here when deciding how to manage the tillage regime.
Pigweed seeds are tiny and germinate very shallow depths.
If you're burying the seeds under four inches they won't germinate, and they'll decay after a few years about two to three years.
So if Palmer or waterhemp plants are seen in the field and are allowed to mature and drop seed consider plowing to bury the seeds at least four inches deep.
Keep in mind that if you till again the next year, or again that season, many of the seeds will be brought to the shallow soil again and are able to germinate.
This is when reduced tillage may come in if that's a possibility for this specific farm.
Reducing tillage would allow these deeply buried seeds to remain buried, and any new seeds that fall would remain on top of the soil which means that they can be eliminated by predatory insects, or unfavorable weather conditions.
Penn State has many resources available for those interested in reducing tillage in organic farms.
Feel free to contact your county extension agent or weed science specialist for more information on managing tillage practices for pigweed control.
Number five, if you see any Palmer or waterhemp plants pop up during the season, go in and pull them out.
Pull them out by hand, or using a hoe.
Don't leave the plant lying in the field because it can re-root.
Instead, carry it to the edge of the field and bury or burn them so that the seeds don't have a chance to migrate to other areas of the farm.
Although this may be time-consuming depending on how many plants there are in the field, it's well worth it and necessary as each plant can produce up to a million seeds that will germinate the next year leading to a serious infestation.
Number six, if there are more than a few plants that persist after early harvest, they should be mechanically removed by cultivation or by mowing or discing.
If the plants are over six inches tall and are too big to be effectively cultivated they should be mowed or disced to prevent seed production.
Since invasive pigweeds like Palmer and waterhemp can regrow after mowing and then quickly form seed heads repeated mowing may be necessary.
Palmer and waterhemp both grow quickly and produce up to a million seeds per plant allowing them to severely infest a field within a couple of years.
However, the seeds in the seed bank will also only survive for a couple of years in the soil.
So, if the plants are eliminated before they produce seed the weed population can be well managed within a few years.
This weed requires a zero tolerance policy not letting any plants survive to produce seed.
After harvest is an important time to go in and remove any remaining mature pigweed plants so that the seeds don't fall in the soil.
To recap, here are some of the most important things to remember in order to ensure successful management of Palmer and waterhemp in organic systems.
These seeds are transported to new fields by seed, feed, manure, and equipment.
Take care to make sure anything brought onto the farm doesn't contain these weed seeds.
Diversify crop rotations that include early season crops like winter cereals, cover crops, and other crops that are planted early and harvested before Palmer produces seed.
Consider crops that can be mowed, like perennial forage.
Optimized competition by using varieties that develop canopies quickly by planting narrow rows, if possible and maintaining high soil fertility.
Combine deep tillage and no-till to bury seeds at least four inches in the soil and then leave them on the soil surface.
After early harvest, mow plants that are over six inches tall to prevent seed bank establishment.
Lastly, institute a zero tolerance policy to weed control when it comes to these two problem weeds.
Palmer Amaranth and waterhemp may be in a field near you.
Developing a proactive management plan now and using the recommendations in this video will save time and money later.
Talk to your county extension educator.
They can help you find out if these weeds are in your area, help identify a suspect weed, or offer further recommendations.
For further resources on herbicide resistant pigweeds visit our website.
While you're here, be sure to watch our other Learn Now videos on Herbicide Resistant Pigweed including Weed ID, Proper Prevention and Disposal Practices, and Management in Horticultural and Organic Systems.
Thanks for watching.
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