The results from over 600 samples of grasses collected from two sampling regions are reported, including a total of 87 farms that were near mid-northern Canterbury near Lincoln (52 farms) and southern Canterbury near Timaru (35 farms). Each farm would often have more than one crop type, sampled fields included wheat (61 farms), barley (30 farms) and white clover (21), but we included <2 farm fields with linseed, beets (Beta vulgaris L.), and peas. The following common weedy grasses were found as survivors prior to harvest on a sizeable number of the 87 farms we visited: A. fatua (52 farms), B. diandrus (16), B. hordeaceus (19), B. catharticus (29), Lolium spp. for suspected hybrids (23), L. multiflorum (38), L. perenne (46), Lolium spp. (occurred on a total 57 farms), P. minor (17) and V. bromoides (14). Only three broadleaf weeds were common, S. asper and S. oleraceus were found on 27 farms and Achillea millefolium L. (yarrow) on five. All other weeds were collected from three or fewer farms. Some seed samples had poor germination and were not included in our tests of resistance. Results are presented for the common grasses surviving label rate applications of different post-emergent herbicides but grouped by weed genus and herbicide modes-of-action. More detailed results broken down by farm and herbicide active ingredients are provided in the supplementary materials (S1 Appendix). Farms with plants (within each weed genus) surviving treatment with one or more herbicides for a mode-of-action are indicated in Table 2 . A spatial presentation of the same data indicates where the farms with resistance were located ( Fig 1 ), and resistance to herbicides in the given mode-of-action ( Fig 2 ).
Before our survey was started, we believed there was a low prevalence of herbicide resistance in wheat and barley, for example, in our funding proposal for this work we estimated that 5–10% of farms would contain resistant weeds. Only three previous publications documented cases of Lolium spp. or A. fatua resistant to ALS and ACCase herbicides in wheat and barley crops in New Zealand [11,12,28]. There was also a case of resistance of S. media in an oat crop (Avena sativa L.) . However, we found that resistance is common overall (48%), and particularly for grass weeds on wheat and barley farms with plants surviving on between 23% and 36% of the farms after treatments with ACCase- and ALS-inhibiting herbicides, respectively. This suggests that this issue was historically under-reported by farmers, agricultural chemical suppliers, and consultants as well as under-investigated by scientists.
We also report results from a few other weeds supplied to us by industry agronomists that were tested. S. media samples were sourced from ryegrass rotation (near Matamata on the North Island) and one sample from Ashburton in the South Island from a field planted in clover and ryegrass were treated with flumetsulam 30 g ai/ha (Preside ® ) and a paraffinic oil surfactant (0.5%), and chlorsulfuron 20 g ai/ha (AgPro Chloro ® ) with a non-ionic surfactant (0.25%). D. sanguinalis supplied to us from two maize (Zea mays L.) farms near Matamata on the North Island was treated with nicosulfuron 60 g ai/ha with paraffinic oil surfactant (0.5%) (S1 Appendix).
Plants grown at Massey University
45000 ha) and barley (
This study is the first random survey carried out in New Zealand to detect herbicide resistance for a range of arable weeds and estimate its prevalence on wheat and barley farms. Such surveys may not have been implemented previously because costs of these investigations are prohibitive, an earlier estimate suggested it could cost as much as 759 NZD (New Zealand Dollars) per farm . However, we estimated costs of approximately 370 NZD per farm in the second year of these surveys. After randomly sampling of >20% wheat and barley farms in the targeted regions, resistance was detected in 48% of the sampled farms, this is likely to be lower than the true rate since detection is imperfect . The basis for this argument is that we could have missed individual resistant plants in a field and because we focused on up to ten plants in just two fields per farm, depending on which weeds were available to collectors prior to harvest [18,19]. Our sampling rate is better suited to the detection of outcrossing weed species but could miss some self-pollinating species [18,19]. Species previously identified as having an elevated risk of developing herbicide resistance in wheat and barley fields were confirmed resistant, i.e., L. multiflorum, L. perenne, A. fatua, P. minor, and S. media . Bromus catharticus was resistant to ALS-inhibiting herbicides in this study, a first globally , but identified as medium to low risk by Ngow et al .
Weed control programs that use herbicides have proven to be cost-effective for improving yields of staple crops by an average of 30% , and typically provide a 2-4-fold economic return . They are also a key element in no-till planting programs for wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) farms in New Zealand that improve soil structure and prevent soil loss through erosion . Nevertheless, farmer practices worldwide have led to the selection of weeds with infrequent genetic mutations that confer resistance to the herbicides, allowing weeds to escape control, reproduce and form resistant populations . Globally, herbicide resistance is common in arable crops such as wheat (344 cases and 83 species) and barley (87 cases, 47 species) . Based on worldwide patterns of resistance, Ngow et al  identified 16 species with a high risk of developing resistance in New Zealand wheat and barley fields (eight were grasses Avena fatua L., A. sterilis L., Digitaria sanguinalis (L.) Scop., Echinochloa crus-galli (L.) P. Beauv., Lolium multiflorum Lam., L. perenne L., Phalaris minor Retz., and Poa annua L.; these grasses were in the top 10 for risk of developing herbicide resistance).
Depending on the availability of adequate seed in a sample, the number of herbicides that could be tested changed. Herbicides were tried in the priority order shown for each taxon ( Table 1 ). For example, a sample of 60 seeds would only be tested against the top three to five priority herbicides ( Table 1 ) as we tried to maintain between 10 and 25 seeds per treatment. The same priority order was used for samples treated at Massey University (see below). All herbicide treatments were applied using the highest recommended label rate for the herbicide being tested ( Table 1 ) with a moving belt sprayer using a single TeeJet TT11002 fan nozzle at 200 kPa, positioned 440 mm above the top of the pots/trays to apply 200 L/ha. Glyphosate was tested because it is commonly used prior to planting for seed bed preparation. We included isoproturon on V. bromoides which is a photosystem II inhibitor because industry consultants thought it is effective, even though this species is not mentioned on the herbicide label. In 2019, up to 12 pots were grouped into trays (22cm x 35cm x 5 cm) nursery for spraying. Up to about 22 nursery trays per herbicide treatment could be sprayed with a single herbicide at any given time due to the 1 L capacity of the spray tank reservoir. Only one or two susceptible controls (in individual pots) were used per herbicide treatment. In 2020, as mentioned above seeds were planted out in lanes across each tray with a susceptible control in one of the lanes per propagation tray. Sonchus asper and S. oleraceus from the random surveys were treated with chlorsulfuron 20 g ai/ha (AgPro Chloro ® ) with a non-ionic surfactant (0.1%).
BVN continues online with our October to April program of free public presentations. These virtual events occur on the 4th Tuesday of every month at 7:30 pm. Watch the “Events” tab on the BVN website for details about how to register and find links to previous program recordings. Let’s hope one day soon you will see a note that we gather in-person gain. Until then…
Jen Reimer || Tuesday, October 27, 2020
This past summer BVN volunteered to assist Louis with monitoring Mountain Pine Beetle (Dendroctonus ponderosae) activity in the Canmore area. Louis Price is a forest health officer with Alberta Environment and Parks. He will present information on the status of Mountain Pine Beetle activity in the lower Bow Valley and possibly tell some tales of other ecosystem interactions going on around us in the forests of Southern Alberta.
Louis Price || Tuesday, November 24, 2020
The photo (below) of the tail of an Audubon’s Warbler from our last session is interesting. The outer left tail feather (L6) is missing most of the white typically found on these feathers. White feathers seem to be structurally weaker than darker colours, and wear more rapidly. I have also seen this occur in the secondary feathers of woodpeckers.
BANFF, Alta. — Producers across Canada battle at least 77 herbicide-resistant weeds every year.
“We are seeing an increase in resistant weeds and a stagnation of the modes of action we have to manage those weeds,” said Charles Geddes of Agriculture Canada.
“If we are cutting these patches too late we could have a viable seed and a portion of that seed could survive rumen digestion,” Geddes said.