Soybean Background

• Soybean is an essential crop in the United States
• Used for food and oil
  • Primarily for feeding livestock and producing cooking oil

A new pest

• In 2011, there were reports of an unidentified orange larvae on the stems of damaged soybeans after a hailstorm
• Entomologists received reports of larvae infestations in 2018 for an unknown species causing significant damage

A new pest

• Initial surveys indicated the infestation was in Minnesota, Iowa, South Dakota, and Nebraska
• As of 2020, the insect was identified in 114 counties, now including Missouri

A new pest

• Initially found on damaged plants at the end of the growing season, causing little economic concern
• In 2018, an infestation warranted further concerns when a sample of damaged plants from earlier in the growing season had no other detectable plant diseases
• Insects were identified as a new species in the Resseliella genus
• Females lay eggs in damaged parts of soybean stems and larvae eat away at the stem

Possible solutions

• At this time, there are no guaranteed methods for preventing damage due to soybean gall midge

• One possible method, the subject of today’s talk, is to cover the stems of soybeans with dirt

  • A process known as hilling

Generalized Linear Mixed Models

Generalized Linear Mixed Models

Unhilling Study

Two primary research questions:

1. How does unhilling affect total SGM larvae counts? / Does having a preventative measure earlier in the growing season decrease SGM larvae counts?

2. How does unhilling affect soybean growth/yield?

• Field organized into two rows and two columns, with each section acting as a block

• Seven treatments of unhilling dates approximately two weeks apart (one left unhilled at the start of the study as a control)

• For (1), larvae counts were taken approximately every two weeks

• For (2), growth/yield metrics were taken at the end of the growing season

Unhilling Study: Fitted Model (1)

where

• \(\eta\) is the intercept

• \(\tau_i\) is the effect of the \(i^{th}\) unhilling date

• \(S_j\) is the effect of the \(j^{th}\) sample date

• \((\tau S)_{ij}\) is the interaction effect between the \(i^{th}\) unhilling date and the \(j^{th}\) sample date

• \(S(B\tau)_{ijk}\) is the effect of the \(i^{th}\) unhilling date, \(j^{th}\) sample date, and the \(k^{th}\) field section (block)

• Response distribution: \(y_{ijk}| S(B\tau)_{ijk}\sim Poisson(\lambda_{ijk})\)

• Link function: \(\eta_{ijk}=\log(\lambda_{ijk})\)

Unhilling Study: Results (1)

Differences marked with an asterisk (*) are considered marginally significant. There were no other significant simple effect differences for each sample date.

Unhilling Study: Results (1)

Larger treatment numbers denote a later date for unhilling. Trends indicate that unhilling earlier in the season have larger counts of SGM larvae.

Unhilling Study: Fitted Model (2)

The full model is presented for the five collected responses. These are count of soybean nodes, pods, seeds, and plant height and seed weight.

Where

• \(\eta\) is the intercept

• \(B_i\sim N(0, \sigma^2_B)\) is the effect of the \(i^{th}\) field section (block)

• \(\tau_j\) is the effect of the \(j^{th}\) unhilling date

• \((B\tau)_{ij}\sim N(0, \sigma^2_{B\tau})\) is the interaction effect of the \(i^{th}\) field section and the \(j^{th}\) unhilling date

• \(\epsilon_{ijk}\sim N(0, \sigma^2_e)\) is the random error of the \(i^{th}\) field section, \(j^{th}\) unhilling date, and the \(k^{th}\) plant

The model is then fit the these specifications

Unhilling Study: Results (2) - Soybean Height

Unhilling Study: Results (2) - Soybean Height

Unhilling Study: Results (2) - Soybean Seed Count

Unhilling Study: Results (2) - Soybean Seed Count

Discussion

Future work

STAT 930 Reflection