Can Minimal Cultivation Reduce Your Herbicide Input?

John Jemison, University of Maine Cooperative Extension Water Quality and Soil Specialist

About this time of the year, you are probably thinking about next year’s field season. If you are like most people, you are probably looking for ways to cut cost. Herbicides can be a significant component to your production scheme. So, if there is a way to reduce cost, without taking too much time, it might be worth trying. I would like you to consider cultivation as a possible way to cut cost.

Based on discussions with dairy producers in Maine, we have found significant interest in cultivation methods for corn. We found that most producers are either interested in either cultivation using no herbicides, or reducing rates of herbicides by including some cultivation in their operation. Based on this interest, we set up a study this summer to look at how much you could reduce herbicides by including some cultivation into the corn production process. We evaluated three cultivation strategies (no cultivation, tine cultivation at spike stage followed by row cultivation at the V-6 growth stage, and two standard row cultivations at growth stages V3 and V6). Within each of these cultivation strategies, we applied different rates of the herbicide Broadstrike + Dual (no herbicide, 1/3^rd rate, 2/3^rd rate, or the full recommended rate). We evaluated weed control and corn silage yields.

Early Results

We rated weed populations in middle June (corn growth stage V2) and early July (V5) to evaluate the effect of the tine and row cultivations. When we compared the single tine cultivation to no cultivation at V2, we found no real difference in weed control. Timing is critical with all cultivation, but it is particularly important with tine cultivation. You need to cultivate either just before corn emergence or as corn starts to emerge. I think we used the tine cultivator just a bit too early in 1998. Last year in another experiment, we cultivated a bit too late which shows one of the difficulties with this type of cultivator. With a tine cultivator, you have to cultivate when the soil is dry and the weeds are just beginning to emerge. That is often a hard combination to find in New England. Too early, you just move around the soil; too late, and the tines will not remove the weeds.

However, row cultivation at the V-3 leaf stage was important at reducing weed populations (Figure 1.) With no cultivation, if we increased the herbicide rate up to the full-recommended rate, we found improved weed control. There was no surprise there. However, if we used a row cultivator when the plants were small, we found equally effective weed control at 1/3^rd the recommended herbicide rate as we did with the full rate. That was a big surprise.

Following that weed rating, we did a final row cultivation at the V-6 growth stage. That cultivation significantly reduced weed populations that had emerged in the row since the last cultivation. We took weed biomass samples at canopy closure to assess the effect of the final cultivation. We found that through cultivation with no herbicide we were able to reduce weed biomass over 50% (Figure 2). Cultivation also reduced weed pressure at the 1/3^rd herbicide rate. Even though there is not much evidence for improved control with cultivation where herbicides are applied at the 2/3^rd or full rate, there may still be other agronomic reasons to consider one pass with a cultivator. More on that later.

Most producers can live with a few weeds if the impact on yield is not significant. The most interesting finding was that yields with cultivation and reduced rates of herbicide were very similar to those where we used full recommended rates. In fact, the highest yield (24.5 tons/ac) was found with the two row cultivations and the 1/3^rd rate of herbicide (Figure 3). We found only 21.2 tons with no cultivation and the full herbicide treatment.

You might be wondering why this can work. Cultivation does more than simply reduce weed populations. The mixing process adds oxygen into the soil, improves water infiltration, and loosens up heavy soil. It can also stimulate nitrogen mineralization at a time when the crop can effectively utilize it. The soil used in the study was a fairly heavy silt loam. This could make the difference particularly in a wet early summer like we had last year.

Key Points To Remember About Cultivation

• Cultivation can help you control weeds better than with herbicides alone

• Tine cultivation can help control in-row weeds, but timing is critical

• Row cultivation may allow you to reduce herbicide rates with a year

• Row cultivation can loosen heavy soils, increase oxygen in the root system and stimulate mineralization at a time when plants can utilize the nitrogen

• This combined with good crop rotation could be a way to significantly reduce the cost of crop production.