Cabbage – Release of the Caterpillar Egg Parasite

Trichogramma pretiosum

 

What was the purpose of this experiment?

 

We wanted to determine if the commercially available wasp, Trichogramma pretiosum could control cabbage caterpillars when released in home gardens.

 

What gardeners did?

 

  • Gardeners planted a plot Golden Acre cabbage.
  • Half the gardeners released 2 cards of wasp pupae in their garden twice each week for 12 weeks.
  • Half the gardeners did not release any wasps.  Their gardens served as the untreated controls.
  • The number of cabbage worms found on each cabbage was counted each week by both groups of gardeners.

 

What did the gardeners find?

 

  • Gardens where Trichogramma wasps were released had 1/6 the maximum number of caterpillars per cabbage as the untreated control plots (Fig. 1).
  • Cabbage in plots where Trichogramma wasps did not have enough caterpillars to cause significant yield reduction.
  • Gardens in the untreated control plots had enough caterpillars to cause significant yield reduction.

 

What is the bottom line?

 

  • Releasing Trichogramma wasps provides acceptable control in the home garden.
  • The current cost of the weekly Trichogramma ($10) releases makes this practice economically unacceptable for small plots of cabbage.
  • Further research is needed to determine if control can be achieved with fewer releases.
  • Research is needed to reduce the price of Trichogramma shipments. 

 

Figure 1.  Effects of releasing Trichogramma pretiosum on the average numbers of caterpillars > 3/4 inch seen on each cabbage plant over the course of the summer.

 

 

Potato – Use of Straw Mulch to Provide Habitat for Natural Enemies of Potatoes

 

What was the purpose of this experiment?

 

We wanted to determine if straw mulch creates a habitat in the garden that increases the number of insect predators.

 

What gardeners did?

 

  • Gardeners grew plots of Katahdin potatoes in 2 rows that were a minimum of 6 ft long and 2 ft wide.  Each plot was separated by 20 ft or were in separate gardens.
  • Half the plots were mulched to a depth of 2 inches with wheat straw.
  • Two pitfall traps, loaded with “pet friendly” antifreeze, were placed in each potato plot to collect predators walking along the soil surface over the course of a week.
  • Traps were replaced and sent off to the Illinois Natural History Survey for processing each week from mid-May through the first week in August.

 

What did the gardeners find?

 

  • Gardens mulched with straw contained more individuals and a greater diversity of predators.
  • 15 families of beetles were found in mulched plots compared with 9 in those without mulch.
    • More rove and ground beetles tended to be in mulched plots.
    • Fewer sap beetles were found in mulched plots.
  • Twice as many harvestmen (=daddy long legs) spiders were in mulched plots.
  • Four times as many millipedes were present in mulched plots.

 

What is the bottom line?

 

  • Mulching with straw provides an attractive home for many natural enemies of insect pests.  Several reasons have been suggested:
    • Shade protects many dark colored insects that feed at night (rove and ground beetles)
    • Moisture provides habitat for millipedes.
    • Straw strands provides structural complexity for spiders (harvestmen)
  • Studies are needed to test the ability of these natural enemies control leaf feeding. pests.  Suggest an experiment

 

 

Release of the Nematode, Steinernema carpocapsae to Control Iris Borer

 

What was the purpose of this experiment?

 

We wanted to determine if the commercially available nematode Steinernema carpocapsae could be used to control Iris borer in the home garden

 

What gardeners did?

 

  • Gardeners with a history of Iris borers in their gardens volunteered for this experiment.
  • Gardeners identified 4 square foot plots separated by a minimum of 8 feet.
  • In early June half the plots were treated with nematodes, and half the plots were treated with water to serve as the untreated controls.
  • Samples of soil were sent to the laboratory 3 days after treatment to determine whether nematodes that were released were alive.
  • Iris plots were excavated between July 15 and August 1 to determine the number of iris attacked in treated and control plots. 

 

What did the gardeners find?

 

·        Live Steinernema carpocapsae nematodes were found in the soil of 22 of the 29 home gardeners (76%) who applied the product to the soil in June.

·        Research conducted over 2 years in 50 home garden plots showed small but statistically insignificant reduction in the amount of damage caused by iris borer (Figure 2)

·        Despite concerns of home gardeners, incidence of iris borer in home gardens was generally low (<15%).

 

What is the bottom line?

 

·        Live nematodes can be effectively purchased and released for use in home gardens.

·        Iris borer populations were not substantially reduced by homeowner treatments.

·        Low average levels of iris borer in home gardens suggest that Iris borer is not a serious problem for most homeowners.

 


Figure 2.  Effects of entomphagous nematode, Steinernema carpocapsae, and a water control on populations of iris borer in home garden plots.