Download Microsoft Word - AgMemo insert #1 harvest weed management

Harvest weed management
Peter Newman, Alex Douglas and Sally Peltzer
Weeds Research Officers, Geraldton, Katanning and Albany
Copyright © Western Australian Agriculture Authority, 2010
Welcome to the first state wide edition of Weed Management. These Weed
Management sections of the Ag Memo will appear three to four times per year
across the state over the next three years. The information presented will be
relevant to the time of year and will focus on Integrated Weed Management (IWM)
of herbicide resistant weeds in cropping situations. This initiative is a part of a
GRDC funded project with Peter Newman as the principle researcher based in the
Geraldton DAFWA office. The information presented will focus on lessons learnt
from the Northern Agricultural Region, including case studies, as well as more
general information about herbicide resistance and its occurrence throughout the
state.
Clearly this information will reach a range of growers throughout the state from those
who are living with full blown herbicide resistance through to those who are relatively
new to cropping and are living in the honeymoon period where the herbicides are still
working. These growers do, however, have one thing in common. If they choose to
use only herbicides to manage weeds, the weeds will win. Growers that are taking
an integrated approach are proving that it works and many of their case studies will
feature in future articles. Peter Newman, Geraldton ph. 9956 8563
Weed seeds at harvest – spread, catch, divert, burn or destroy?
A wise man once said to me; “It seems ironic that we spend all year spraying weeds
with thousands of dollars worth of herbicides only to turn around and spread all of the
surviving weed seeds evenly all over the paddock”. Targeting weed seed has been
identified as a key strategy in controlling resistant annual weed populations. The
control of these populations is a numbers game and weed seed removal is an
excellent strategy that can be used to keep the numbers low. A number of
techniques can be used to destroy / remove at least 50% of weed seeds of annual
ryegrass and wild radish populations at harvest. But is this enough to make an
impact on the weed seed bank and the development of herbicide resistance?
Computer modelling suggests that 50% seed removal at harvest will not fix a weed
control system that is not working. It will, however, have a significant impact where a
weed seed bank is being maintained or increasing slowly. The figure below shows
the results of computer simulation with the RIM (Ryegrass Integrated Management)
program developed by WAHRI at UWA. This demonstrates that for a continuous
cropping system where only 90% ryegrass control is achieved each year the seed
bank of the ryegrass increases slowly over a 10 year period. By adding a chaff cart
or baler at harvest that removes 50% and 75% of the ryegrass seeds in the paddock
each year respectively, the ryegrass seed bank is eroded over time. Our aim for
managing resistant weeds should simply be to continually reduce weed seed banks.
Removing weed seeds at harvest is probably the most important non-herbicide weed
management tool to achieve this.
2000
nil
chaff cart 50%
baler 75%
2
1500
/m
Ryegrass seeds in soil
RIM computer simulation of ryegrass seedbank lupin:
wheat rotation
Trifluralin every year 90% control
1000
500
0
0
1
2
3
4
5
6
7
8
9 10
Year
Figure 1 Computer simulation using RIM program showing the predicted
ryegrass seed bank (seeds /m2) in a lupin wheat rotation where 90% weed
control is achieved each year for three harvest options; Nil (conventional
harvest), Chaff cart removing 50% of weed seeds in each crop, or a baler
towed behind the header removing 75% of the weed seeds in each crop.
Which tool?
Table 1 Summary of some of the main harvest weed seed management tools.
Tool
Set up cost
Pros
Cons
$100 to
Windrow
Cheap to get into. No
Involves burning. Wind
$500
burning
loss of harvest efficiency.
erosion risk. Difficult in
Very effective.
cereals. Time consuming
in autumn. Nutrient
banding.
Chaff Cart
$30K to
Minimises area of
Reduces harvest
$50K
paddock burnt. Can
efficiency. Cost. Burning
provide feed source for
heaps in autumn is very
livestock.
time consuming.
$400 to
Chaff
Cheap. No burning. No
Must have fully matched
diversion onto $5000
loss of harvest efficiency.
tramline system.
tramlines
Reduces dust during
Unproven. High weed
summer spraying.
density on tramlines
About
Harrington
No burning. Nothing to
Cost. Extra piece of
Destructor
$100K
do after harvest. Very
machinery.
(possible
robust machine – can
release 2012
handle house bricks!
/ 2013)
About
Baling
No Burning. Additional
Cost. Extra nutritional
everything – $150K to
income from bales. Most
drain on soil. Need a
$200K
Glenvar
effective tool on the
market for bales. Handling
system
market.
of lots of bales.
Chaff carts / Harrington Destructor / Diversion onto tramlines should be able to
remove 70 to 80% of the ryegrass / wild radish that enters the harvester. However,
due to ryegrass shedding / lodging this represents approximately 50% of the total
weed seeds in the paddock.
The baler and windrow burning should be able to remove 95% of ryegrass and wild
radish that enters the front of the harvester. This represents approximately 70% of
weed seeds in the paddock. Walsh and Parker (2002).
Case study – Rod Birch, Coorow
Rod Birch from Coorow is demonstrating that it is possible to maintain continuous
crop while managing resistant ryegrass by targeting weed seeds. Rod is a big
believer in the use of windrow burning as a tool and he is one of the pioneers in the
area.
350
Ryegrass / m 2
300
250
200
150
100
50
0
2001
2002
2003
2004
2005
Figure 2 Birch #5 - Ryegrass plants (in August) / m
2006
2007
2008
2009
2
Table 2 Control used on crops over specific years.
Year
2001
2002
2003
2004
2005
2006
2007
2008
2009
Crop
Lupin
Wheat
Canola
Wheat
Lupin
Wheat
Canola
Wheat
Lupin
Ryegrass Herbicide
Simazine & Fusion
Trifluralin + SU
Atrazine & Select
Trifluralin + SU
Simazine & Motsa
Trifluralin + SU
Atrazine – Sacrificed with glyphosate
Trifluralin + SU
Simazine & Select
Non herbicide
Burn narrow windrows
Burn narrow windrows
Burn narrow windrows
Burn narrow windrows
Burn narrow windrows
Dry year - no windrow burn
Burn narrow windrows
Will make narrow windrows
Rod’s comments
This paddock was out of control with ryegrass in the 1990’s so we decided to take an
aggressive approach to herbicide resistance and use as many tools as possible. We
have burnt header windrows for a number of years. I think of the header as a big
seed collector. The trick to burning wheat windrows without burning the whole
paddock is to harvest very low and to not graze the paddock at all. Livestock will
disturb the windrows too much. We ensure that the header never ever leaves its
track so we end up with one big un-disturbed spiral of windrow. We use a chute
mounted to the back of the header to make narrow (600mm wide) windrow. Burning
windrows has caused some issues with potassium levels in some paddocks. We
observed strips of high nutrition in cereal crops. We subsequently worked with Bill
Bowden (DAFWA) to identify that Potassium was the issue and have adjusted our
fertiliser program to address this problem.
We are also finding that trifluralin works best when it has maximum contact with the
soil. Burning windrows reduces trash which aids this soil contact. The lupin / wheat /
canola / wheat rotation is a good one for ryegrass management because it enables
some different weed management each year. For example, we swath the canola and
often crop top in the lupin phase. In the wheat phase we aim to grow a competitive
crop and use trifluralin.
Making narrow windrows this harvest
For growers who want to make a start at weed seed management this harvest,
windrow burning is probably the most achievable option given that harvest will soon
be upon us. A good place to start will be in canola and / or lupin crops as it is easier
to contain the burn to the windrow. It is necessary to mount some sort of chute to the
rear of the header to concentrate all of the trash and straw into a narrow windrow.
The opening at the bottom of the chute should be 500 to 600mm wide depending on
how thick the crop is. Your model of header will determine what sort of chute is
appropriate. If you would like more information in this area please email me at
[email protected] and I will send you some photos of chute designs
for a range of header types. If you do mount a chute to your header, remember to
reverse immediately when you stop to avoid the header blocking up. See Rod
Birch’s comments above relating to successful windrow burning. We will follow up
with more information in Autumn relating to conditions to achieve a successful burn.
Peter Newman, Research Officer, Geraldton ph. 9956 8563
What is herbicide resistance?
Herbicide resistance is the inherited ability of an individual plant to survive a
herbicide application that would kill a normal population of the same species.
Within any weed population there may be some plants that already contain a
rare gene that enables them to survive the application of a particular herbicide
that would normally kill this species. Genetic variation may alter physiological
traits that enable herbicide uptake, translocation and activation at the site of
action (target-site resistance). Alternatively, changes may influence the plant’s
ability to detoxify herbicides, or enable transport to a site within the plant where
the herbicide is not lethal (Non-target-site resistance). Each time the herbicide
is applied, susceptible plants die and those with resistance survive.
Factors affecting the development of resistance include:
 Selection Pressure – Every time herbicide is used, susceptible individuals
are killed and resistant individuals survive. The greater the number of
susceptible individuals killed by the herbicide, the higher the selection
pressure.
 Initial frequency of the resistance gene within a population – The more
resistant genes in a population the quicker resistance develops. For example
the resistance frequency can be as high as 1 plant in 10 000 (Group B) and
as rare as 1 plant in 100,000,000 (Group M, eg glyphosate)
 Weed density – the higher the number of weeds, the greater likelihood that a
particular resistance gene is present.
Sally Peltzer, DAFWA, Albany [email protected]