Broadleaf Weed Control in Autumn

Broadleaf Weed Control in Autumn.

With the approach of cool Autumn temperatures, it’s one of the best times for broadleaf weed control in Australia. The best broadleaf weed herbicides tend to be very effective at this time as it’s when Winter annuals and cool-season perennials get ready for the cold months ahead.

The problem with summer broadleaf weed control is that herbicides are not effective at killing the entire plant. In contrast, in the Autumn broadleaf weeds work to store energy in their root system rather than trying to promote top growth. This means they are more susceptible to herbicides.

March to April is often the ideal time to overseed (this depends on where you are, time and use constraints) as temperatures are perfect for cool-season turf growth.

If you have compact soils, then a coring or aeration program helps relieve any compaction. It also helps create conditions that don’t favour weeds like Asthma Weed, Bindweed, Chickweed, Dandelions, Wireweed, Plantains, Speedwell and White Clover. These are all Indicator weeds of compaction.

As temperatures fall, cool season turf starts to green up. You should focus aeration work on areas where the most broadleaf weeds like Plantain and Wireweed exist. Also, as cool temperatures close in, weeds like Chickweed and Henbit start to germinate.

Cultural Broadleaf Weed Control in the Autumn.

Doing the right thing by your turf is the first step to reduce weed populations. So make sure you have the right turf grass for your  site and budget. Also, take into consideration any shade issues.

For example, why choose a grass that doesn’t like frost if you are in Canberra.

Every turf type has an optimal height of cut, and water and fertiliser requirement. You want a dense, healthy turf, as weeds find it difficult to get a foothold in healthy, competitive turf. By simply doing this, you help manage weed populations.

In areas where broadleaf weeds are a problem, if you mow as often as is practical it tends to remove the seed head of weeds. Remove the clippings when you do this, or you will just spread weed seeds all over the area.

Once you identify a weed, you can then develop a management plan. This should go beyond simply applying a herbicide like  “Bow and Arrow” because everyone else does.

If the problem is just a few individual plants, then hand-pulling isn’t going to be a total pain. Keep in mind that with perennial weeds, you need to make sure that you remove the entire root system to stop any re-growth.

Perennial broadleaf weeds include:

• Buchan Weed.
• Carrot Weed.
• Catsear.
• Creeping Buttercup.
• Creeping Charlie.
• Creeping Mallow.
• Creeping Oxalis.
• Cudweed.
• Dandelion.
• Deadnettle.
• Dichondra.
• Dock Weed.
• Field Bindweed.
• Fleabane.
• Gazania.
• Heal All.
• Hydrocotyle.
• Japanese Knotweed.
• Khakiweed.
• Lambstongue.
• Little Ironweed.
• Oriental False Hawksbeard.
• Oxeye Daisy.
• Petty Spurge.
• Praxelis.
• Red Clover.
• Singapore Daisy.
• Sowthistle.
• Speedwell.
• Stinkvine.
• Swinecress.
• Tridax Daisy.
• White Clover.

Instigating cultural control in the Autumn is a great way to reduce weed populations, as herbicides should be seen as a last resort.

In Autumn, if you have a lot of actively growing weeds, then post-emergents give good results. However, you must always make sure that you follow the label.

Getting The Best Results.

Apply post emergent herbicides in the right conditions to get the best broadleaf weed control.

• In the early morning. It is often less windy in the early morning than later in the day. If you spray early in the day, it reduces the chances of spray drift into sensitive areas.
• Use herbicides when air temperatures are 13 to 26°C.
• You get the best results when the weeds are not under stress. This means that you want weeds to be growing well so that any systemic herbicide moves through the entire weed.
• Make sure you spray when there is good soil moisture.
• As a general rule don’t use these if you expect rain within 24 hours. Check the label for specific recommendations.
• Don’t mow for a few days before or after use. If you don’t mow before you apply, this ensures that there is the largest possible leaf area for herbicide uptake.

As mentioned earlier as Winter approaches, broadleaf weeds like Dandelion and Ground Ivy, move carbohydrates to the roots. This process also helps post-emergents move around the weed, and so increases their effective control.

Finally, realise that cool-season turfgrass (ryegrass, bent, fescue) grows best in the Autumn. This means it will tend to quickly fill in bare areas left by dead weeds.

Several herbicides give effective Autumn post-emergent broadleaf weed control of common weeds like White Clover, Dandelions, and Plantains.

In the Autumn, you can also use pre-emergent herbicides to prevent future problems with broadleaf weeds. To work properly you need to apply these before weeds germinate. Any existing weeds you can control with the methods we discuss earlier.

Conduct any cultural practices as per the label directions. When in doubt, hollow tine or de-thatch before you apply a pre-emergent.

Water or irrigate after use as per the label directions.

Pre-emergent Herbicides for Broadleaf Weed Control.

Several pre-emergents are available for broadleaf weed control. These include:

• Dithiopyr (Dimension). Dithiopyr controls Chickweed, and Winter Grass if you use it before weeds emerge.
• Pendimethalin (ProForce Battalia 435). Pendimethalin controls Chickweed, Henbit, Knotweed, Prostrate Spurge, Purslane, White Clover, Medic, Soursob and Yellow Woodsorrel if you use it before weeds emerge.
• Prodiamine (ProForce Onset 10GR). Prodiamine controls Common Chickweed, Henbit, Knotweed, Prostrate Spurge, Purslane, and Yellow Woodsorrel.
• Oxadiazon (ProForce Echelon and ProForce Echelon Duo). Echelon Duo controls Summer grass, Crowsfoot grass, Winter grass and Creeping oxalis and also African black beetle, Argentinian scarab and billbug. This means that one application prevents weeds and insect pests.
• Isoxaben (Gallery). Although not registered for home garden use, if you manage nursery tree stock this is an excellent pre-emergent for broadleaf weed control. It has a massive control spectrum, but no effect on grass weeds. The image below is 6 months after application. No broadleaf weeds but grass weeds are going well.

Autumn Broadleaf Weed Control with Post-emergents.

• Dicamba (Various). Dicamba, a benzoic acid, works in a similar way to 2,4-D and MCPA. It works well against Knotweed, Purslane, and Spurge but does not control Buckhorn or Broadleaf Plantains well.

Dicamba is mobile in the soil, so it’s important that you read and follow the label directions to stop off target issues. This is because tree roots may pick up dicamba and it will injure sensitive species.

Dicamba is not safe to use on Buffalo grass.

• 2,4-D Amine: is a common post-emergent broadleaf herbicide. It does not control grass weeds, and it is systemic. Uptake is via the leaf, and it then moves through the plant. The result is uncontrolled growth, and stems of weeds curl-over, their leaves wither and the weed eventually dies.
• MCPA: MCPA is a selective herbicide that controls broad-leaf weeds, but not grass weeds. It mimicks the action of a plant growth hormone. This results in uncontrolled growth, and then death in susceptible weeds. MCPA is more selective than 2,4-D, but you need less 2,4-D to control annual weeds.
• Quinclorac (Quinstar): Quinclorac works against White Clover, Dandelion, and Summer grass. To get the best results use this with a methylated seed oil like ProForce Voltage MSO. This destroys the cuticle of the target weed and helps the herbicide enter the plant.
• Topramezone (Pylex): This effects susceptible weeds and causes bleaching due to chlorophyll loss. It works well on Chickweed, and Clover but you cannot use this on warm season turf.

Post-Emergent Mixes.

Many post-emergent combination products offer a huge increase in range of weeds taht you can control. 

• MCPA + Bromoxynil + Dicamba (Broadcide). This controls Bindy-eye, Capeweed, Carrot weed, Catsear, Caustic weed, Clovers, Common plantain, Creeping buttercup, Cudweed, Dandelion, Horseweed, Funnel weed, Jo-Jo (Onehunga), Thistles, Three-cornered Jack (Doublegee), and Wood sorrel (Oxalis spp.)
• MCPA + Dicamba (Contra M). This controls Bindy-Eye, Capeweed, Catsear, Chickweed, Clovers, Cotula, Creeping Oxalis, Cudweeds, Dandelion, Dock, Fleabanes, Fumitory, Jo-Jo (Onehunga), Lamb’s Tongue, Medics, Mustards, Narrow-leaved Plantain, Pearlwort, Pennywort, Peppercress, Radish, Scarlet Pimpernel, Slender Thistle, Soldier Thistle, Spear Thistle, Toad Rush, Variegated Thistle, Wild Turnip, Wireweed.
• Bromoxynil + MCPA (ProForce Weed Blast MA). This has contact and systemic activity. It gives quick control of broadleaf weeds, with results in 7 to 14 days. This mix works well on Bindy-eye, Jo-Jo (Onehunga), Cudweed, Capeweed, Catsear, Creeping Buttercup,  Dandelion, Thistles, Amaranth, Fleabane, Clover, Hairy Bittercress, Oxalis, and Plantains.
• Dicamba + Prosulfuron (Casper Herbicide): It is a selective and systemic herbicide that kills annual and perennial broadleaf weeds. Uptake is via the leaves and roots of plants, and it then moves around the weed. It inhibits the growth of buds, causes the stems to swell, and then kills all plant tissues.

Casper is great against: Bindii, Burr Medic, Cat’s Ear, Creeping Oxalis, Chickweed, Cotula, Curled Dock, Dandelion, Fleabane, Khaki Weed, Lambs Tongue/Plantain, Pennywort, White Clover, Blackberry Nightshade, Milk Thistle, Clover, and Wireweed.

• Diflufenican + Clopyralid + MCPA (ProForce Warhead Trio). Warhead Trio works well against Bindii, Capeweed, Cats Ear, Creeping Oxalis, Cudweed, Plantain, and White Clover. Be aware that you can’t reseed for 6 weeks after you use this and similar products, as it inhibits seed germination. It works slowly so you often don’t see the results on some weeds for up to 6 weeks.

In Summary.

Hopefully, having read this you are in a better position to know your target weeds and your best options to control them. Not all herbicides have the same spectrum of broadleaf weed control. This means that it is important to know what herbicides can and cannot do, so that you get the best possible results and don’t waste your money.

Are Hose on Packs Your best Option?

Lawn and garden hose-on packs (or ready-to-use applicators) are great to apply fertilisers, herbicides, and soil wetters. However, they are not perfect and have some big disadvantages:

• Uneven Application. Hose-on packs rely on water pressure to dilute and distribute their contents. If your water pressure is poor, it means you get uneven coverage. Some areas will get too much product, which causes damage from over application, while other areas get too little, which will give poor results.
• Limited Control Over the Amount you Apply. If you use hose on packs you are not able to “tweak” the application. This is an issue for lawns that have specific nutrient deficiencies or pest problems that need a more targeted approach.
• Waste of Product. Hose-on packs often apply more product than you need. This means a lot of waste, and isn’t good for the environment as it increases the potential for runoff.
• Inefficient on Large Lawns. Hose-on packs are mainly for small to medium-size lawns. For large areas, these are not user friendly as they have limited coverage, and can quickly become expensive.
• Potential for Equipment Failure. These packs can clog, leak, or break, if you don’t use or maintain them properly.
• If your spraying regularly these are not cost effective. While they are very convenient, hose-on packs are more expensive than if you buy concentrates and use a knapsack sprayer.
• Short shelf Life. Once you open them, hose-on packs may not store well. Exposure to the air or moisture can cause the product to break down. This measn that you may need to use the entire pack, even if only part of it is required.
• Lack of Flexibility. Hose-on packs are pre-mixed for specific uses. This means there is no flexibility to mix other products.
• Are they actually Suitable for foliar use? A water volume of 8L per 100 m2 or under is regarded as being suitable for foliars. Anything over this volume and you are applying products to the soil.
• When you use a hose on pack how much water do they apply? How can the same hose on pack effectively apply a SOIL wetting agent and a FOLIAR fertiliser if it applies the same amount of water?

Alternatives to Hose on Packs.

To overcome these problems, consider:

• Backpack sprayers for better control and more flexibility.
• Use concentrates to mix your own solution. This means you can apply what you want and need, when you want to. This also saves you money in the long run.
• While hose-on packs offer convenience, their disadvantages make them better suited for occasional or small-scale use rather than regular lawn care on large areas.