Determining the Biggest Bang for our (Time) Buck: Dealing with Fall Brassica Diseases in High Humidity Environments

We have previously used all of these cultural controls already on our operation. Our goal in this trial was to test and assess them individually against varying spray intensities to determine their relative impact.

Results of pest covers:

Row Cover—10 of the 12 trial spray iterations included treatment zones with and without row cover after the initial two to three weeks of critical establishment.

ProtekNet—our 2021 fall lettuce trial (for aster yellows control) showed better airflow, plant health, and yield over row cover. Additionally, we can spray through the netting without removal, unlike row cover. Given its price point, we were unsure if it’s worth using on lower value/wider spaced crops. For all trial iterations, a zone was sealed under ProtekNet, with scouting and spraying happening through the netting. We hope to assess whether the added cost of the netting is offset by plant health and reduced application times.

Uncovered—due to pest pressure, we haven’t grown uncovered fall brassicas for almost a decade. Part of this trial was to see if improved organic pesticides (Entrust and Evergreen) could allow for uncovered production.

• Statistically, we did not see a huge efficacy difference between the three cover options in terms of disease reduction. But surprisingly, plantings without row cover had greater net return per unit, and were more cost effective than we thought. It was significantly faster to plant, cultivate, and spray on iterations with no row cover or netting (duh!). Since so much of our variable cost comes from labor, saving time by not having to deal with moving anything did offset the lower yields of uncovered plantings.
• We observed that on a cost basis, for most zones the more expensive netting did not pay for itself relative to row cover, even factoring in that row cover is only used once and the netting many times. Scouting and spraying through the net was faster, but installation time costs were higher. There was an exception as direct seeded brassicas did have higher net yield and income under the more ventilated Proteknet. It was unclear if this result was because the netting itself is less effective, or because the row cover we use covers 3 beds at a time (rather than 1 with the netting), thus reducing labor management costs.
• Also on a cost/unit basis, open uncovered trials did not perform terribly, as long as the variety selection was a shorter season cultivar, and there were reasonable numbers of spray applications. However, open/uncovered beds did reduce overall yield (they just remained most profitable because their costs were so low), and should thus be further assessed. Open plantings generally outperformed netting on a cost/unit basis, while netting performed better on a total yield basis.
• We felt like our status quo—row cover—remained the best default option mixing some protection with cost/labor effectiveness. However, we feel like based on the uncovered zone data, we should remove covers earlier and just add in a pesticide application. Netting however still has appeal to us for direct seeded crops, pending further trials.

Plant spacing.

We normally transplant two rows per bed 24" apart, at in-row distances of 14” for broccoli and 19” for cauliflower (and 1” for radishes). We trialed both 2” spacing in radishes, and 19”/24” for broccoli and cauliflower to assess if the cost to use extra space pays off in terms of disease control and yield.

• We observed no yield differences in our wider spaced zones. Our suspicion is that is because we had already widened to optimal spacing in past years, additional spacing provided no additional benefit.

Aisles.

The three large brassica iterations each include an aisle section “mulched” with landscape fabric as opposed to bare ground to explore if the landscape fabric keeps water from splashing pathogens up from the soil. (Aisle landscape fabric is uneconomic for small brassicas.)

• At the highest level of disease pressure, landscape fabric was the difference between getting some yield and nothing. It was also the only statistically significant conclusion in this trial.
• In our Alternaria apocalypse trial field, landscape fabric correlated so strongly with higher yields and profitability that it altered the statistical significance of landscape fabric across all four trial fields. In a wet, disease-y year, it makes economic sense to prioritize using fabric.
• We only used new landscape fabric, as we were unsure if there might be impact from disease carry over if using older fabric. This might change the economics of the fabric in future years, if it's vectoring disease.

Isolation.

For harvest convenience/irrigation, we plant fall crops in larger blocks. Starting in 2021, we began switching to a rotational system of smaller blocks of the most disease prone crops and planned for each large brassica iteration to include a zone with an isolated planting of one bed at a distance from any other brassicas. 

• Due to an excessively dry start to the summer and all our irrigation mains and headers in dire need elsewhere, we were unable to plant the isolation zones.
• Interestingly, all the zones were hit at the same time with Alternaria (so it didn’t seem that distance matters). However, later plantings of broccoli that were touching our most infested zone (2) did not show much infection. This leads us to wonder to what extent timing has on disease pressure over proximity.

The three fungicide frequency application intensities trialed across the cultural controls are:

• High—every 7 to 9 days, and after every rainstorm over ¾”, from the week after planting until harvest.
• Moderate—every 14 to 21 days, down to 10 days if scouting suggests. Our norm, largely due to weather conditions making additional applications feel like a waste of time.
• Low/No Spray—zero to one timed spray application as scouting suggests. In these past years, because of rain, some fall brassicas received zero applications and still produced, which makes us question if any organic fungicide application is actually effective against very damp weather?

Our intent was not to trial individual product efficacy, but rather investigate if overall frequency of fungicide application impacts the cultural controls. We used a rotation of Howler, OSO, Carb-O-Nator, and Cueva from planting until harvest began (Zones 1 and 3), the Alternaria apocalypse wiped out the crop (Zone 2), or the crop was mature enough control was no longer necessary (Zone 4). All applications include the sticker-spreader Miller Nu-Film P.

• We did not see clear efficacy of any products against Alternaria (and had minimal black rot, thanks to the dry summer). It was faster to spray on iterations without row cover, but we found the row cover easier to manage than the netting (thanks to it being wider, cheaper so we weren't paranoid about damaging it, and something we have more practice at handling).
• There was no added benefit to spraying more in 2022, either in terms of net yield or net income.
• Our data showed that spraying more than our normal two-week interval did not pay off with higher yields. Net income was slightly better actually the less we sprayed, thus answering our question—is it worth hammering crops with more frequent spray applications to reduce disease—in the negative. For direct seeded brassicas, data suggests stopping fungicide applications entirely.
• However, we were pleasantly surprised at how well our pesticide applications controlled flea beetles on the uncovered zones in some of the later plantings. We saw strong reductions in pest numbers using Entrust (spinosad), even in the zone with very high pest pressure. However, we saw very weak correlation between spraying more frequent fungicides and higher yield of marketable product.
• We felt like there was more impact from variety selection and timing than from organic fungicides. However, we also felt that we should re-trial a tighter fungicide rotation of the two that showed better efficacy in 2022 extension trials (OSO and Badge).

Changes and Adjustments:

We did have to adjust the trial during the growing season.

Our first major hiccup was that we planned and budgeted for this project in summer and fall 2021, but we implemented this project after early 2022’s jump in pricing, labor, and interest rates. We saw supply cost increases and a tighter than normal labor market. We had to tighten up the size of our treatment zones due to high cost on the Proteknet in particular, and shorter staffing to a lesser degree. But as initial zones were three times as long as they ended up being, they may have been too large to start out with!

The second adjustment was that due to an excessively dry spring and early summer, we had to make two field changes. First, we needed double irrigation lines elsewhere in key fields, so we weren’t able to install the distant isolation zones as all the mainlines were in use. However, we observed that all brassicas on the farm that were hit by Alternaria showed signs at the same time, regardless of location or relative isolation. In fact, we had abutting plantings (where the leaves actually touched) where later untreated plantings didn't have much disease (more on that in future trial section).

This dry weather also led us to plant 3 large brassica rounds and only 1 direct seeded round. We generally observe greater disease pressure in the larger cultivars, and we were concerned the direct seeded plantings would be too healthy to show results this season. Little did we know the weather would flip!

2022 was an odd weather year, with a pattern that is becoming too common here in NY: excessively dry first half of summer flipping to an excessively wet second half. Unusually, we had a high level of Alternaria in the fall brassicas but essentially no other diseases hit these crops (nor did we seem other diseases in non-treatment areas), so we aren’t sure if the treatments would have had more impact if the 2022 disease load was more diverse.

The final hiccup in the trial was that half our farm got Covid quite bad in September during the peak of the trial, and it lingered for the next month or more, which significantly impacted our outreach plans!

Finally, on a minor note, we switched from managing our data with AirTable to using old fashioned paper forms, as we didn't want employees to have to use their personal electronics in such wet conditions. This was fine during the season, but created a huge paperwork burden that really delayed data assessment later in the year! 

Measured or Projected Farm Changes:

We had imagined that more intensive management would result in lower plant insect and disease pressure, and thus in higher net yields (and presumably higher net income).

What we saw was that less management can lead to greater net profit (which makes sense since we were spending so much less labor in those treatments during low-disease parts of the season). Yields in these less managed treatments were not always of adequate quality or were too low to be space efficient (we have access to unlimited space). However, as disease pressure increases, more intensive cultural practices and management pays off.

We were surprised to learn broccoli and cauliflower were more profitable than our previously created enterprise budget (as long as yields were decent) as we had considered them loss leaders in the best-case scenario. Under high disease pressure situations, they are still catastrophic money losers. Timing seems critical to keep in mind when making such management decisions. We plant many successions of individual crops, but as a CSA-focused farm, assess and manage them as averages. We should be looking at each one individually as timing alone seems to be our key variable.

Our main farm change from this trial was better understanding of the true cost and impact of our management around spray frequency and high labor cultural controls. This understanding is leading us to use landscape fabric, row covers, and netting, as well as spray more strategically for pests and less for disease.

For 2023, this supported our decision to change our market mix away from CSA and towards more wholesale and smaller markets, where we can minimize our staffing costs, reduce our fall brassica production, and make time on the farm to better assess several other of our crops and markets closely. Ultimately, we believe this will make us more financially and personally sustainable in our operations as we specialize a bit more into crops where we know we have better margins and less production pressures.