HERBICIDE APPLICATION NATIONAL FACT SHEET OCTOBER 2019 Effective Double Knock herbicide applications By using a Double Knock approach in fallow paddocks, growers have a reliable technique to control difficult weeds while also assisting in the management of herbicide resistance. What is a Double Knock? Always refer to the registered KEY POINTS A Double Knock (sometimes called product label. sequential applications) is where n Double Knock herbicide growers apply two different weed Why use a Double Knock strategies are critical to reducing control tactics to a single flush of application? weed seed banks. weeds to stop any survivors from the Growers have adopted the Double Knock n May delay the selection for first application setting seed. The approach for the following reasons: glyphosate resistance, where tactics do not need to be herbicides. n to achieve very high levels of weed Double Knock applications are Cultivation, heavy grazing or fire could control that are required to stop seed routinely introduced before also be used as a second knock. set and drive down weed seed banks; resistance is present. The most common Double Knock n to delay the onset of herbicide approach is to apply a systemic resistance; however, this will only n Optimal timing between herbicide (for example Groups A, occur if growers implement the applications is dependent upon I or M are frequently used) when strategy well before resistance the herbicides used and the conditions are favourable for has developed in that field; weeds being targeted. maximum translocation, and then n to provide improved levels of control n Where possible, always target follow it with a contact herbicide of difficult-to-control weeds such small weeds to ensure reliable such as the bipyridyls (Group L). as feathertop Rhodes and windmill performance. Table 1 represents some herbicide grass, fleabane and sowthistle; and n n Attention to herbicide application products used for Double Knock to overcome physical or parameters will improve applications. This is not intended to be biological incompatibility of consistency of results. an exhaustive list of available options. certain herbicide mixtures. TABLE 1 Examples of some herbicides suitable for Double Knock applications. Fleabane at an ideal stage to commence a Herbicide group Active ingredient (primary registered brand name) Double Knock herbicide program. A haloxyfop (Verdict®); propaquizafop (Shogun®); quizalofop (Targa®) G* butafenacil (B-Power®); carfentrazone-ethyl (Hammer®); flumioxazin (Valor®); oxyfluorfen (Goal®); saflufenacil (Sharpen®) I 2,4-D (Amicide®); clopyralid (Lontrel®); dicamba (Cadence®); fluroxypyr (Starane®); fluroxypyr + aminopyralid (Hotshot®); halauxifen + fluroxypyr (Pixxaro®); picloram + 2,4-D (Tordon® 75-D); picloram + triclopyr (Grazon® DS); picloram + 2,4-D + aminopyralid (FallowBoss® Tordon®); picloram + triclopyr + aminopyralid (Grazon® Extra) L* paraquat (Gramoxone®); paraquat + diquat (Spray.Seed®) M glyphosate (Roundup®) N* glufosinate (Basta®) PHOTO: BRUCE WILSON Q amitrole (Amitrole T) Q+L* amitrole + paraquat (Alliance®) *Herbicide groups G, L, N and Q+L have Modes of Action that work by rapid contact activity, so they are normally preferred as the second application when used in a Double Knock program. Haloxyfop (PER12941 – QLD only), quizalofop (PER13460 – NSW only). GRDC Level 4 | 4 National Circuit, Barton ACT 2600 | PO Box 5367, Kingston ACT 2604 grdc.com.au 1 T +61 2 6166 4500 F +61 2 6166 4599 E [email protected] PHOTO: MARK CONGREVE, ICAN GRAINS ORANA ALLIANCE PHOTO: MAURIE STREET, Do not let fallow weeds get out of control. In addition to robbing the fallow of soil moisture, weeds such Poor control of fleabane, where boom height was too as these large sowthistle have already started to return seed to the seed bank and will be very difficult to low for full spray coverage of a paraquat application. control, even with a Double Knock application. move easily through the plant. They are How to maximise the Most advisers recommend that if rain is performance of Double therefore best targeted at small plants forecast, it is usually preferable to apply Knock applications only, and they must have a high level the second application a day or two To obtain the high levels of weed of coverage to achieve good results. earlier than the ideal timing, rather than control required in a fallow, the first risk the possibility of being kept off the paddock for an extended period of time herbicide application must be able What is the best due to wet conditions. This is especially to achieve a robust level of control application timing? important when using Group L products in its own right. Therefore weeds It is important to plan to Double Knock. as the second knock, as these cannot be targeted by the first knock should To obtain maximum performance applied by air. ideally be small (pre-tillering for when using two different herbicides grass weeds and still in the rosette as a Double Knock, growers Poor control with the second knock is stage for broadleaf weeds) and not will generally apply the second often due to the weeds becoming too suffering from stress (for example, application before the full effect of large or too stressed or not having frost, too hot, too wet, too dry or the first application is evident. enough photosynthetic material to allow damaged by insects or grazing). Robust Poor results are regularly seen bipyridyl herbicides to work effectively. application rates and good coverage where growers only apply the second If climatic conditions have prevented are required to achieve the maximum knock as an afterthought or when they application of the second application performance on difficult-to-kill weeds. have delayed application until the first for an extended period and plants The second application in a Double application is showing signs of recovery. have started to regrow, then the use Knock program is then applied to further increase levels of control, TABLE 2 Suggested minimum spray volumes for bipyridyl (Group L) ensuring their are no survivors. Often herbicide application. the Double Knock approach will use a systemic herbicide for the first Spray quality Recommended water volume application and a fast-acting contact Fine Avoid using due to the risk of spray drift. herbicide for the second application. Medium Spray volume of 50 to 75L/ha will normally give acceptable results. Where a systemic herbicide is used for the first application, it is important to Use water rates at the lower end of the range on small weeds and in allow a few days for the first herbicide situations where coverage is ideal to move throughout the weed before (i.e. low populations with minimal shading). applying the subsequent contact Coarse Spray volume of 75 to 100L/ha will normally give acceptable results. herbicide that will quickly shut down any further possibility of herbicide Use water rates at the lower end of the range on small weeds and in situations where coverage is ideal translocation. Contact products, such (i.e. low populations with minimal shading). as a Group L bipyridyl herbicide, do not 2 grdc.com.au of a non-chemical Double Knock TABLE 3 Suggested intervals for some common Double Knock tactic, such as cultivation or fire, may herbicide combinations. be more successful in achieving the Second Recommended objective of preventing seed set. Weed First application application timing Comments The interval between herbicide Broadleaf weeds applications will affect the efficacy of the Double Knock. The ideal Most broadleaf weeds glyphosate Group L 7 to 21 days. interval depends upon a number (for example, Optimal timing is paraquat) generally 10 to of factors, which include: 14 days n the type of herbicide being used Difficult to control Group I (for Group L 7 to 21 days. If interval is greater for each application (systemic broadleaf weeds such example, (for example, Optimal timing is than 14 days, use or contact herbicides); as fleabane Amicide® paraquat) with or generally 7 to maximum label rates n the species being targeted (Conyza bonariensis) Advance, without saflufenacil 10 days of Group L herbicide (generally shorter intervals for Tordon®, (Sharpen®) grasses than broadleaf weeds); herbicides) with or without n the size and age of the weeds; and glyphosate n temperature and available moisture. As a general rule, the smaller Difficult to control glyphosate 2,4-D 2 to 4 days Recommended to broadleaf weeds split applications the weed, the less time it will take such as sowthistle/ due to biological for the first systemic herbicide milkthistle incompatibility product to translocate throughout (Sonchus oleraceus) between 2,4-D the plant. Employ intervals at and glyphosate. As the shorter end of the range. both products are systemic, the interval needs to be short. Application parameters when using contact glyphosate Group L 7 to 21 days. Only target small (for example, Optimal timing is rosettes herbicides as the second paraquat) with or generally 7 to knock without saflufenacil 10 days Contact herbicides require excellent (Sharpen®) plant coverage to achieve good results as they are not translocated within the Grass weeds plant. Historically growers achieved Most grass weeds glyphosate Group L 4 to 14 days. This strategy may this coverage by using smaller spray including: Annual (for example, Optimal timing not be effective on ryegrass (Lolium paraquat) is generally 5 to glyphosate resistant droplets in the fine to medium range. rigidum), Barnyard 7 days populations. With the increased focus on spray drift grass, (Echinochloa reduction, fine droplets are no longer colona & E. crus-galli) recommended. When using medium Feathertop Rhodes propaquizafop Group L 7 to 14 days. Target small, actively to coarse spray quality for contact grass (Chloris virgata) (Shogun®) (for example, Optimal timing is growing weeds for herbicides applied as the second paraquat) generally 7 to 3 leaf to early tiller. knock, increase the spray volume to 10 days Refer to Shogun® ensure that there are enough spray label.