Systemic Crop Signaling for Automatic Recognition of Transplanted Lettuce and Tomato under Different Levels of Sunlight for Early Season Weed Control

Wen-Hao Su

doi:10.3390/challe11020023

Abstract

Conventional cultivation works to control weeds between the rows, but it ignores the weeds in crop rows which are most competitive with crops. Many vegetable crops still require manual removal of intra-row weeds not otherwise controlled by herbicides or conventional cultivation. The increasing labor costs of weed control and the continued emergences of herbicide-resistant weeds are threatening grower ability to manage weeds and maintain profitability. Intra-row weeders are commercially available but work best in low weed populations. One strategy for rapid weed crop differentiation is to utilize a machine-detectable compound to mark a crop. This paper proposes a new systemic plant signaling technology that can create machine-readable crops to facilitate the automated removal of intra-row weeds in early growth stages. Rhodamine B (Rh–B) is an efficient systemic compound to label crop plants due to its membrane permeability and unique fluorescent properties. The project involves applying solutions of Rh–B at 60 ppm to the roots of lettuce and tomato plants prior to transplantation to evaluate Rh–B persistence in plants under different levels of sunlight. Lettuce and tomato seedlings with the systemic Rh–B should be reliably recognized during their early growth stages. An intelligent robot is expected to be developed to identify the locations of plants based on the systemic signal inside. Reduced light treatments should help to alleviate the photodegradation of Rh–B in plants. After being exposed to full sunlight for 27 days, the systemic Rh–B would be detectable in tomato branches and lettuce ribs, and these plants are tolerant to root treatments with this fluorescent compound. This paper describes the project background and plan as well as the anticipated contributions of the research to allow the machine vision system to reliably identify the crop plants, and thus showing technical feasibility for outdoor weed control.

Highlights

Weeds in lettuce and tomatoes are hard to control because of labor shortages, the increasing cost of manual weeding and limited herbicide options
After a 27-day outdoor exposure, the Rhodamine B (Rh–B) fluorescence on the entire adaxial surfaces of both the lettuce and tomato plants under reduced sunlight (20% or 50%) irradiations should show higher photostability than that under 100% sunlight
Rh–B is used as a temporary systemic signal to indicate the location of lettuce and tomato plants grown under different levels of sunlight

Summary

Introduction

Weeds in lettuce and tomatoes are hard to control because of labor shortages, the increasing cost of manual weeding and limited herbicide options. Lettuce is very sensitive to weed competition. Weeds must be effectively controlled before lettuce is to be harvested. Effective weed control prevents weeds from competing with crops for sunlight and nutrients, which is of great significance for ensuring crop yields. Typical weed control techniques such as non-chemical, chemical and mechanical methods cannot reliably remove weeds from crops [1]. Cover crops planted during the fallow period have limited restrictions on the growth of weeds in the upcoming vegetable crop season and may have a negative impact on the growth of main crops [2].

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