Strategies for orchard weed management hard economic situations

Brad Hanson, UC Cooperative Extension Specialist, UC Davis

I recently participated in a UCCE meeting focused on orchard management decision making when times are hard. This was in the context of the current low walnut prices facing producers in the state, but given the cyclic nature of agriculture could easily apply to other perennial crops as the ups and downs of agricultural commodities respond to domestic and international markets.

When thinking about where weed control costs can be cut and gaming out the consequences of reduced weed management interventions, I think it’s useful to step back and remember why we’re controlling weeds in the orchard in the first place.

Generally, in tree crops like walnuts, we control weeds to:

  1. reduce competition for resources, particularly water and nutrients,
  2. reduce weed interference with crop management operations and practices, especially irrigation,
  3. reduce plants and debris that can interfere with nut sweeping and harvest operations,
  4. be good farmers and stewards of the land and the orchard

In considering “lean” weed control programs, I tend to first think about weed competition in making decision about where to cut back. In a young orchard, say the first 3-5 years after planting, competition from weeds could be really problematic and might set the growth of the trees back in such a way that there are long-term impacts. I probably wouldn’t cut back too much in those young orchards because of that risk. On the other hand, weed competition is probably not so bad in a well-established orchard; sure, weeds will reduce water and fertilizer use efficiency to a degree but probably won’t directly hurt the crop too much or cause long-term impacts on tree health.

Next, I think about weeds most likely to interfere with my irrigation system; tall weeds that block sprinkler patterns or interfere with water flow in some way and need to be managed somehow. In this case the weed problem is indirect, but still a problem if it results in poor irrigation and fertilizer distribution. I’d focus here on making sure irrigation uniformity remains reasonable in spite of the orchard being a bit weedier than normal.

Wherever possible, consider the weed’s life cycle and try to time any weed management practices to reduce seed set because those seeds will be the source of weeds for years into the future. Mowing or tillage operations can be timed to be implemented before mature seeds are formed. Likewise, if you’ve got significant problems with perennial weeds like Johnsongrass, bermudagrass, or nutsedges, you might focus resources to reduce their spread and proliferation.

So, if we’re going to cut back somewhere on weed control practices, what are some thoughts and approaches?

First of all, weed identification, which is always an important part of good weed management programs, is even more important if you’re deciding which weeds have to be controlled and which ones you might be able to live with. Not all weeds are equally problematic. I’d focus here on the perennial weeds, the new invaders, the hard-seeded species with long soil life, and the weeds that will result in large debris that will persist to harvest.

Second, stretch your retreatment intervals. This basically is reducing weed management intensity by mowing and spraying less frequently (and getting used to a few more weeds) in order to save a few trips though the orchard. I’d time any operation to reduce weed seed set but tolerate a little bit of age-appropriate competition. Consider here the year-round cost; if you skip a mowing but then have to spray and mow twice to clean up before harvest you might not actually save much at all.

In the reduce intensity category, I’d also suggest reducing the width of the tree row spray strips.  Blocking a nozzle or two on the inside of the spray boom could reduce the treated area by 1/3 to ½; I’d consider the width of your mower and spray the minimal strip but still be able to mow in a single pass. This also has implications in less-lean times when we are thinking about general herbicide-reduction goals in the orchard. I think that doing a very good job on half the amount of area is a better strategy than doing a mediocre job on the whole area because the tree row is where competition will be most problematic and where weeds will interfere most with irrigation delivery. Also, in the reduced intensity category, think about your tank-mix programs and if every component is really needed; I’d argue that a second (or third or fourth) product added to the tank-mix to increase control from 95 to 99% may be one that could be left out in difficult times.

I’m occasionally asked about generic herbicides vs the main branded products because several of our important herbicide active ingredients are off-patent and distributed under many product names. Usually, when I’ve done head-to-head testing, I’ve found little, if any, performance differences. My caution here is to make sure that you’re really making an apples-to-apples comparison with regard to formulation concentration and surfactant packages. Of course, there are programs and packaging deals to be had in making your overall orchard management pesticide decisions so be sure to talk to your PCA and retailer about overall costs.

I summarized my thoughts on navigating lean weed management decision making as:

  • Don’t skimp on weed control in the young trees because of long-term impacts from competition.
  • Really think about the weeds you have in orchard and their real impact on the orchard and operations.
  • Reduce the intensely managed area by narrowing spray strips.
  • Reduce treatment intensity and stretch retreatment intervals.

Reducing weed control in orchards during difficult economic times is possible but comes with some tradeoffs. Give up a little in the short term and let it get a little ugly in terms of weediness but reduce the long-term impacts to the degree possible. Focus on maintaining the young orchards, reducing interference with irrigation and harvest, and try to time the weed control practices to minimize weed seed set. Integrated weed management approaches are still key, even when we are forced to move the goal posts due to (hopefully!) short-term economic realities.


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