According to the Department of Agriculture, Fisheries and Forestry (DAFF), weeds are estimated to cost agriculture $4.344 billion in an average year including both control expenditures and residual agricultural losses. The estimated total cost of weeds is 10% of the Local Value of Production (LVP) of all affected industries (beef, sheep meat, and all crops) therefore best practice weed control is a must for profitable farming/cropping operations.
Weed Control in Horticultural row crops
Looking specifically at horticultural row crops, lets breakdown some key issues caused by weeds:
- Weeds compete directly with fruit trees for needed water, nutrients, and light, especially in new plantings leading to stunted growth, reduced fruit size and yield with significant economic loss as shown above.
- Weeds can interfere with irrigation by blocking the sprinkler pattern or causing uneven or inefficient irrigation. Latterly this has been eliminated by using drip lines but these can be damaged by foxes and roos and/or by whipper snippers used in weed control.
- Weeds are known to provide harbour for insect pests as well as rodents (rats and mice) and cover for rabbits thereby facilitating increased costs of insect and rodent control.
- Significant weed cover under trees impedes worker and machine access and causes a WHS safety concern for ladder use.
Weed control Options;
Herbicide use:
Figure 1 and 2. Lilly Pilly shelterbelt with Agave plants (fig. 2) 7 DAT with 200 g/l glufosinate in warm humid summer weather with good soil moisture (SEQLD at 75 ml/15l knapsack in 500 l/Ha water with a TTI1003 nozzle
Weeds included Flaxleaf fleabane, Billy goat weed, Benghal Dayflower, Awnless barnyard grass and Buffel grass
Non-selective herbicides such as glyphosate, paraquat/diquat, and glufosinate are often used as directed sprays near trees and vines ensuring spray doesn’t drift onto crop leaves though shielded/skirted sprayers or air inducted off center nozzles. In vines, glyphosate, given its translocation from leaf to roots in the sap stream, is used early in the season and on mature vines with brown bark. Paraquat or glufosinate are better used later in the growing season given they don’t readily translocate within plants (see in Figure 1& 2 showing no obvious harm to Lilly pillies/Agaves from glufosinate spraying onto weeds around stems).
Don’t forget to include selective herbicides and pre-emergents in your chemical stable to assist with year-round weed management to drive down the dormant weed seedbank in the soil over time, a key objective.
The watch out with herbicidal weed control in young or newly planted seedlings is to adjust label rates according to the size and always follow any WHP’s once at the fruit bearing stage. It is also important to rotate between the different modes of action or use tank mixes with 2 different modes of action to limit the potential for selection of herbicide-resistant weeds over time. Remember to use only clean fresh water free from soil for both glyphosate and paraquat, also avoid hard water with glyphosate (you can’t lather a soap very well in hard water; if water is hard condition with ammonium sulphate).
Mowing/Slashing
Source: https://gason.com.au/product/rapier-vineyard-mower
Weeds can be controlled between the rows with a slasher or mower, with front mounted or rear mounted variants available. Always mow before seed set which will mean a more frequent mowing schedule during spring/wet summers, especially important for prolific seeders such as flaxleaf fleabane with up to 110,000 seeds per plant. Vineyard mowers such as the Australian made Gason Rapier pictured below is popular for inter-row mowing and can be fitted with full side plates for rear discharge of shredded prunings. Gason also do orchard mowers right out to 6.1m cutting widths for row crops with wide inter row spaces.
Cultivation
Cultivation can be used to control annual/biennial weeds and the perennial weed seedlings. Perennial weeds with rhizomes can be exacerbated by cultivation unless the soil is very dry. Also care needs to be taken to not damage tree roots, water lines or cause erosion in heavy rainfall events.
Check out this interrow weeder used in vineyards, https://www.youtube.com/watch?v=KdszETlm0Ts
Robotic or automonous weeders are also now available to save on herbicide usage, labour costs and mundane hand weeding jobs.
Cover crops
Source: https://themacadamia.co.za/2019/06/24/take-cover-protect-your-resources-with-cover-crops/
Cover crops help to build soil health, are water saving and aid in reducing tree stress. A cover crop is a crop seeded or encouraged as natural plant cover as an investment in soil fertility and not for revenue. Most cover crops are grasses, legumes, brassicas or a mixture and protect bare soil while improving soil physical, chemical, and biological properties and limiting erosion. Vegetable growers use brassica species, such as mustard, radish and rocket as cover crops to help suppress soilborne diseases, whilst work is being done by Adelaide university with medics and ryegrass as under vine crops to assist vine health and soil biology and the results look very promising.
Mulches
Young avocado trees with mulch in WA (Source: https://www.agric.wa.gov.au/avocados/avocado-industry-regulation-western-australia)
Weeds in the rows can be controlled using mulches such as sugarcane tops, mill mud, cereal straw, lucerne hay or composted wood chips etc. around young trees. Apply mulches with no weeds present to prevent weed germination and growth. Mulches assist moisture retention, help growth with essential nutirients and protect roots from temperature extremes. Avoid uncomposted mulches infested with weeds and don’t heap mulch around the stems of trees to limit collar rot potential. Note not all mulches are suitable for row crops, ie for avocados you need a coarse mulch with a carbon to nitrogen (C:N ratio) from 20 to 100, see https://avocado.org.au/best-practice-resource/growing/mulching/#using (requires subscription)
Biosecurity/Hygiene
Last but not least is the need to implement a set of measures to protect your vineyard/orchard from the entry, establishment and spread of unwanted weeds, pests and diseases.
Summary
In summary an integrated approach to weed control in your orchard or vineyard utilising as many controls as possible in tandem together will give you the best long term weed control, help to delay chemical resistance issues, aid Workplace health and safety and assist your social license and popularity with your customers.
Author: Jonathan Pearson – Head Trainer
