Companion Planting: A Method for Sustainable Pest Control - Iowa State University

1. Iowa State University, Armstrong and Neely-Kinyon Research and Demonstration Farms ISRF09-12
Companion Planting: A Method for Sustainable
Pest Control
RFR-A9099 The specimens were planted outside on
May 15. Vegetable species were planted at
Leah Riesselman, ag specialist random in two replications that consisted of
Armstrong Research Farm six, 3 × 5 ft blocks, one block for every
companion plant species in addition to a
Introduction control block. A 3-ft walk-way separated
For centuries, companion planting has been each vegetable replication. Transplants were
practiced by many tribal groups throughout then planted according to their individual
the world. Three Sisters is one example of spacing requirements. Switchgrass mulch
companion planting known to Native was applied a week following the transplant
American tribes. Corn, beans, and squash date. Irrigation scheduling was via hand
are grown together, providing high yielding, application and on an as-needed basis.
high-quality crops with a minimal Tomato plants were staked prior to bloom.
environmental impact. Companion planting
has taken a growing interest among today’s Plants were evaluated according to insect
conventional farmers. damage to leaves, flowers, and fruits. No
insecticide or pesticide was used to control
The objectives of this study were to pest outbreaks.
determine if there is an advantage to
intercrop plants for enhanced growth and to Results and Discussion
determine if selected companion plants The spring and summer growing season was
would provide protection against common unseasonably wet and mild at the Armstrong
vegetable pests by methods of trap cropping Research Farm. Consequently, many factors
and biochemical pest suppression. of disease and insect damage arose that
normally wouldn’t occur under typical
Materials and Methods growing conditions. Rainfall total for May
Five vegetable species and five companion was 2.06 in. and just under 6.00 in. for June.
plant species were grown from seed in the Total rainfall for the 4 months of the study
greenhouse for 6 to 10 weeks. The five was 20.42 in.; almost 60% of the yearly
vegetable species and the five companion average of rainfall for Iowa (Figure 1).
plant species included in the study were: Temperatures averaged in the low to middle
broccoli, Brassica oleracea var. botrytis 70s in the months of May and June, and in
Packman; cabbage, Brassica oleracea var. the upper 70s in the months of July and
capitata; lettuce, Lactuca sativa August (Figure 2). During the week of
Buttercrunch; tomato, Lycopersicon June 21, temperatures averaged 90 degrees,
esculentum Celebrity; zuchinni, Cucurbita leading to the bolting and splitting of lettuce,
pepo, marigold, Tagetes spp. African cabbage, and broccoli plots, thus data
Marigold; onion, Allium cepa Red Zeppelin; collection of these three crops ended.
nasturtium, Topaeolum majus; thyme,
Thymus vulgaris; and basil, Ocimum The first sign of cabbage worm, (Pieris
bailicum. rapae), damage to B. oleracea var. capitata
appeared in the control plots on June 9. The

2. Iowa State University, Armstrong and Neely-Kinyon Research and Demonstration Farms ISRF09-12
primary damage consisted of profound leaf completely destroyed and the roots showed
defoliation and larvae burrowing holes into signs of bacterial wilt. On June 9, bacterial
the cabbage head. In addition, fecal matter wilt was present in the onion companion
from cabbage worm and cabbage looper plots. On June 16, juvenile leaves
(Trichoplusia ni) was found. In comparison, reestablished on the zucchini plants in the
on June 23 slight leaf defoliation was found marigold, nasturtium, and thyme plots, and
in the marigold companion plots of cabbage re-growth was delayed in the basil, onion,
due to cabbage looper. The onion, and control plots. Bacterial wilt from striped
nasturtium, basil, and thyme plots had the cucumber beetle spread to the thyme plots
best resistance toward cabbage worm and on July 7. On August 3, a second generation
cabbage looper (Figure 3). of striped cucumber beetles emerged
resulting in moderate leaf skeletonization
Damage from cabbage worm and cabbage and continued spread of bacterial wilt in the
looper also appeared in the broccoli marigold plots.
replications. However, the basil plots were
infested with cabbage worm the earliest and On July 21, squash bug (Anasa tristis) eggs
were the most severe. Control plots showed were found on the underside of the zucchini
some sign of infestation on June 5, but leaves in the basil companion plots. Nine
damage from cabbage loopers was moderate days after the first sign of eggs, squash bug
(Figure 4). The marigold, onion, and nymphs were found in all plots except the
nasturtium plots appeared to have a small nasturtium plots. The first sign of squash
population of cabbage loopers on the bug in the nasturtium plots didn’t appear
broccoli head, but no significant damage until August 11. The marigold plots and the
was evident. The thyme plots showed no nasturtium plots showed the best
sign of pest damage. resistance/tolerance to striped cucumber
beetle and squash bug.
The primary insect that infested L. sativa
Buttercrunch was cabbage looper. The first The only pest that appeared on the tomato
sign of damage appeared on June 15 in the plants was the yellowstriped armyworm
marigold, basil, and control plots (Figure 5). (Spodoptera ornithogalli). The primary
Damage included leaf defoliation and damage consisted of larvae feeding on the
remnants of fecal matter, which made the fruits. Damage first occurred in the marigold
plants unmarketable. The remaining and control plots, followed by the onion and
companion plots of onion, nasturtium, and nasturtium plots. Basil and thyme illustrated
thyme exhibited high resistance to cabbage the best resistance toward S. ornithogalli.
looper damage.
Conclusively, all the control plots showed
Two destructive pests infested the zucchini the most insect and pest damage, which
plots. Initially, striped cucumber beetle indicates any intercropping with a
(Acalymma trivittatum), damage started in companion plant is more advantageous than
all the companion plots except nasturtium none. Thyme, nasturtium, and onion
(Figure 6). On June 5, striped cucumber exhibited the best resistance of cabbage
beetle populations increased, which resulted worm, weevil, and cabbage looper for the
in heavy skeletonization of the flowers and three cole crops (broccoli, cabbage, and
mature leaves. The control plot damage was lettuce). Marigold intercropped with
so severe that all the flowers were zucchini demonstrated the best resistance to

3. Iowa State University, Armstrong and Neely-Kinyon Research and Demonstration Farms ISRF09-12
cucumber beetle, and both marigold and and mild temperatures has an effect on pest
nasturtium had equal resistance to squash resistance.
bug damage. Tomato insect damage was the
least in the basil and thyme plots. Further Acknowledgements
investigation will determine if there is Thanks to Bernard Havlovic, Armstrong
statistical difference in the climatic Research Farm superintendent, and Randy
conditions of the spring and fall growing Breach, ag specialist, for their assistance in
seasons, and whether the unseasonably wet this study.
Figure 1. Weekly rainfall totals for the months of Figure 3. P. rapae and T. ni damage to the cabbage
May, June, July, and August. The total rainfall for plots.
these four months was 20.42 in.; almost 60% of the
average annual total rainfall for Iowa.
Figure 4. Percentage of damage from P. rapae and T.
Figure 2. High and low temperatures for the 2009
ni resistance to broccoli.
growing season.

4. Iowa State University, Armstrong and Neely-Kinyon Research and Demonstration Farms ISRF09-12
Figure 7. Percentage of damage in the tomato
Figure 5. T. ni resistance to lettuce plots. plots from S. ornithogalli.
Figure 6. Comparison of the percentage of
infestation in the zucchini plots from A. trivittatum
and A. tristis.