With so many farmers taking a wait-and-see attitude about planting peanuts, many fields in the Carolinas and Virginia have been out of peanuts for several years.

How the land was managed during its hiatus from peanuts is critical when the decision is made to grow peanuts again.

Over the past five years prices for Virginia market type peanuts have been volatile, but changing in the wrong direction for growers. Price drops have caused a considerable number of growers to drop out of the peanut business completely, while others have held onto equipment and will plant peanuts if the price gets high enough.

Once the decision is made, to plant or not to plant peanuts, growers need to re-assess fields. One important issue to consider is what cropping systems and rotations have been implemented during the past five years, especially in fields suitable for peanuts.

Crop rotation has long been touted as the underpinning of optimum and efficient production of peanuts and other crops. However, the “biological effect” and the “economical effect” do not always match, and for this reason growers often shorten rotations that are more profitable in the near-term, but can have important long-term impacts.

Research has been conducted in North Carolina for the past 10 years to compare and contrast a variety of cropping systems that have peanuts as a central component. These rotations have included peanuts, cotton, corn, soybeans, and tobacco in various combinations.

During this past growing season (2006) these experiments included peanuts planted in all rotations, and this allowed a good comparison of the effect of crop rotation on peanut yield. These results will give an indication of the “biological effect.”

We haven't worked through the “economical effect” of the duration of the experiments; we will have those results later on.

Results were predictable in many ways. The more years between peanut crops the higher the peanut yield. This was the case at Lewiston, Rocky Mount, and at Whiteville, N.C.

Generally, corn and cotton were equally as effective in maintaining peanut yield in the final year of the experiment (Lewiston). Additionally, including one year of tobacco or corn rather than peanuts in the middle of a six-year rotation was equally as effective (Whiteville).

Peanut yield began to drop when either peanuts or soybeans were included, rather than cotton in the rotation sequence (Lewiston and Rocky Mount).

There were also interesting results when looking at variety selection and fumigation with metam sodium for CBR (black root rot.) For example, when the rotation was shortened at Whiteville, CBR increased dramatically when the susceptible variety Gregory was planted, and this increase in disease resulted in lower peanut yields.

In contrast, planting the CBR tolerant variety Perry resulted in consistent yields regardless of rotation length.

The experiment demonstrates the power of rotation and host-plant resistance in maintaining high yields, especially when there is a history of CBR.

The value of fumigation and variety selection are also demonstrated at Lewiston. The variety Gregory often yielded lower than the variety NC 12C, which is partially tolerant of CBR. However, when fumigation was included, the susceptible variety Gregory yielded well regardless of rotation.

Certainly, fumigation is a more expensive approach, but it is an effective approach. In this experiment corn and cotton were effective rotations, although there is certainly concern about the economic value when corn is planted on sandy peanut soils in the Coastal Plain of North Carolina without irrigation.

Soybeans are another issue. Results from Lewiston show the negative effect of soybeans in the rotation on peanut yields. Likewise, peanut yields begin to decrease at a similar pace at Rocky Mount when soybeans or peanuts are included in the rotation rather than cotton.

The bottom line is that soybeans and peanuts are considered the same when it comes to CBR.

These experiments happened to be in fields where CBR was present. While the specific percentage of acreage in the region with CBR is debated, it is considered one of the most damaging diseases because it does not have a “salvage” treatment after planting.

Within a given season, the two methods of controlling or managing CBR are in place after planting, namely fumigation and variety selection. Decisions on these two choices, while more complicated in terms of variety selection (due to other diseases), are directly impacted by rotation.

So, what is the take home message? The answer depends in part on when was the last time you planted peanuts, and did you plant soybeans in the interim while you may have been “out-of-the peanut business?” While planting soybeans won't magically create CBR in fields (although CBR can be seed transmitted, at least with peanuts), soybeans most certainly will keep CBR going.

Growers with relatively long rotations that exclude peanuts, but have soybeans, will need to make important decisions on variety selection and fumigation.

And although not discussed in much detail here, fumigation decreases nematode populations. And for growers with long rotations that may have little or no CBR, fumigation also plays into the equation.

This research was supported by the North Carolina Peanut Growers Association.