Interactions Between Weeds and Other Plant Pests

Bill Johnson

cutworms and chickweeds

no till corn = more problems

cutworms like to lay eggs on something green (winter annual) when it dies they move on to corn

armyworms like specific grasses and then will move

soybean aphid and buckthorn

overwintering host of the aphid (so is kudzu)

soybean aphid was first discovered early 2000’s

• but insecticide sprays are very effective, wisconsin treats nearly every year

Asian Soybean Rust

10-80% yeild loss

legume hosts, Kudzu is most significant (in attached and defoliated leaves)

comes from southern counties

this rust never materialized as a major disease problem for us

goss’s wilt

there are different strains for different crops

it is gram positive bacteria

problematic in 70s and 80s

sporadic cases up till 2006

has spread to 13 states and 2 Canadian provinces

• 2008 discovery in Indiana

44% yield loss

two phases (leaf blight, systemic vascular wilt)

infection of gosses wilt (cmn for corn)

thought to require plant injury like hail or sand blasting

residue born, viable for 10mo in corn residue

seed borne, 1% transmission from seed to seedling in corn

CMN management options

resistant hybrids

alternate hosts (cmn)

shattercane, green foxtail, giant foxtail, yellow foxtail, bristly foxtail

maybe, johnsongrass, ryegrass

cmn move from weeds to corn?

identify weeds with symptoms

apply postemergence herbicide

cmn pops up every so many years

think of hybrid life spans

winter annual weeds and soybean cyst nematodes

henbit and purple deadnettle can support as much scn as a sensitive soybean

the others can support cysts but not on the level of the two mentioned above

can cause anywhere from 15-30% yield reduction even when symptoms are not present

scn management

crop rotation

scn resistant varieties

winter weed management?

*keep in mind the circle of seasons

scn non host growing with host

can drive populations down

scn having two hosts

is similar to one host in the field

SCN main takeaway

get the host out of the field

Bacterial Streaming

can we get goss’s wilt bacteria out of weeds which have had herbicides applied

rainfall splashes bacteria from dead weeds to infest corn

no matter what herbicide was used to control weeds, bacteria could be recovered (was still present and can still infest fields)

scn key points

managing winter annual weeds does not do bulk of work to drive scn populations down, need to grow a nonhost or resistant crop.

soil microorgansims — role in the evolution of glyphosate resistance in weeds

greenhouse and field were eliciting different responses — different micro?

glyphosate MOA

• block esps enzyme in shikimte pathyway

• inhibits aromatic amino acids

  • three in particular

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Dose Response Objectives of resistant and susceptible with and without microbes

horseweed did not have an impact of the material it was grown in

lambsquarter had incredibly high differences in glyphosate dose response

giant ragweed still saw results but much less differences

root colonization study

field soil has higher levels of root colonization

colonies is good it has infected the root

root colonizatin conclusions

horseweeds had minimal root colonization (seen in above ground data as well)

labmbsquarters the colonization was not affected by GS or GR

impact of only disease organisms on the plants

rhizosphere microbial community dynamics

apha diversity index

the amount of diversity in the microorganisms between plants