Remote detection of non-native invasive plant species using geospatial imagery may significantly improve monitoring, planning and management practices by eliminating shortfalls, such as observer bias and accessibility involved in ground-based surveys. The use of remote sensing for accurate mapping invasion extent and pattern offers several advantages, including repeatability, large area coverage, complete instead of sub-sampled assessments and greater cost-effectiveness over ground-based methods. It is critical for locating, early mapping and controlling small infestations before they reach economically prohibitive or ecologically significant levels over larger land areas. This study was designed to explore the ability of hyperspectral imagery for mapping infestation of musk thistle (Carduus nutans) on a native grassland during the preflowering stage in mid-April and during the peak flowering stage in mid-June using the support vector machine classifier and to assess and compare the resulting mapping accuracy for these two distinctive phenological stages. Accuracy assessment revealed that the overall accuracies were 79% and 91% for the classified images at preflowering and peak flowering stages, respectively. These results indicate that repeated detection of the infestation extent, as well as infestation severity or intensity, of this noxious weed in a spatial and temporal context is possible using hyperspectral remote sensing imagery.

Knowledge of crop abiotic and biotic stress is important for optimal irrigation management. While spectral reflectance and infrared thermometry provide a means to quantify crop stress remotely, these measurements can be cumbersome. Computer vision offers an inexpensive way to remotely detect crop stress independent of vegetation cover. This paper presents a technique using computer vision to detect disease stress in wheat. Digital images of differentially stressed wheat were segmented into soil and vegetation pixels using expectation maximization (EM). In the first season, the algorithm to segment vegetation from soil and distinguish between healthy and stressed wheat was developed and tested using digital images taken in the field and later processed on a desktop computer. In the second season, a wireless camera with near real-time computer vision capabilities was tested in conjunction with the conventional camera and desktop computer. For wheat irrigated at different levels and inoculated with wheat streak mosaic virus (WSMV), vegetation hue determined by the EM algorithm showed significant effects from irrigation level and infection. Unstressed wheat had a higher hue (118.32) than stressed wheat (111.34). In the second season, the hue and cover measured by the wireless computer vision sensor showed significant effects from infection (p = 0.0014), as did the conventional camera (p < 0.0001). Vegetation hue obtained through a wireless computer vision system in this study is a viable option for determining biotic crop stress in irrigation scheduling. Such a low-cost system could be suitable for use in the field in automated irrigation scheduling applications.

Mite-vectored virus diseases of wheat are common throughout the Great Plains and cause significant economic losses to growers each year. These diseases are caused by Wheat streak mosaic virus (WSMV), Triticum mosaic virus (TriMV), and Wheat mosaic virus (WMoV), all of which are transmitted by the wheat curl mite (WCM), Aceria tosichella Keifer. New wheat cultivars with tolerance or resistance to WSMV have been released recently, but their widespread cultivation and potential impact on mite-transmitted virus incidence in the Texas Panhandle was unknown. A total of 648 symptomatic wheat samples were collected from 26 counties, predominately in the Texas Panhandle, and tested by enzyme-linked immunosorbent assay (ELISA) for WSMV, TriMV, and WMoV. Samples that tested negative by ELISA were subsequently tested by real-time quantitative PCR (qPCR) for each virus. Approximately 93% of the samples tested by ELISA were positive for WSMV, 43% were positive for TriMV, and 7% were positive for WMoV. Eleven samples tested positive only for TriMV, but none were positive only for WMoV. When samples that tested negative for the different viruses by ELISA were retested by real-time qPCR, detection of each virus was significantly increased. When results of the ELISA test and qPCR were combined, 100% of the 648 samples tested positive for WSMV, approximately 94% were positive for TriMV, and 23% were positive for WMoV. This demonstrated that the incidence of TriMV in the Texas High Plains is much greater than previously reported. The fact that real-time qPCR revealed over a 2-fold increase in the incidence of TriMV and a 3-fold increase in WMoV demonstrated that the ELISA test, which is commonly used by diagnostic laboratories in the Great Plains, should not be used for studies requiring a high degree of sensitivity and accuracy in virus detection. After initial virus infection status was determined, samples that tested positive for WSMV and TriMV were further observed for WCM infestation. A total of 292 samples were inspected and a total of 101 mites were collected from 40 tillers. Individual mites and the tillers from which they were recovered were tested by real-time qPCR to determine how copy numbers of WSMV and TriMV in mites and host tissue compared, and whether the WSMV/TriMV copy number ratio in individual mites was similar to that of the host tissue from which they were collected. In all mites and tillers tested, the WSMV copy number was always higher than that of TriMV and copy numbers of both viruses were always higher in plant tissue than in mites. Although there was a significant correlation between the WSMV/TriMV copy number ratio in plant tissue and in associated mites, the correlation coefficient was very low (r = 0.31, P = 0.0248). In the majority of comparisons, the WSMV/TriMV ratio was higher in individual mites than in the tiller from which they were recovered. The reason for this increase is unknown but indicates that mites may preferentially acquire WSMV from tillers coinfected with WSMV and TriMV, a finding that could have significant implications for virus transmission and disease epidemiology.

Zebra chip (ZC) disease of potato is associated with the putative pathogen ‘Candidatus Liberibacter solanacearum’, which is transmitted by the potato psyllid Bactericera cockerelli (Hem., Triozidae). The present study was initiated to investigate ‘Ca. L. solanacearum’ development during and following typical commercial storage practices. Using bacteriliferous psyllids, Russet Norkotah potato tubers were infested in field cages 14, 10, and 4 days before harvest. Changes in ‘Ca. L. solanacearum’ detection rate, ‘Ca. L. solanacearum’ titer, and concentrations of phenolic compounds were documented throughout storage. ‘Ca. L. solanacearum’ titer continued to increase during storage. Although significant increases in the frequency of ‘Ca. L. solanacearum’ detection were observed in all infestation treatments, the impact of ‘Ca. L. solanacearum’ infection on tuber quality remained comparatively low in plants infected 4 days before harvest, because the majority of the tubers remained asymptomatic. Minimizing storage and retail chain movement durations would help to limit ‘Ca. L. solanacearum’ impact on tuber quality in tubers infected 14 and 10 days before harvest. This study also demonstrated that ‘Ca. L. solanacearum’ can relocate from a newly infected leaf to a tuber in as little as 4 days. Psyllid management is recommended until at least 4 days before green harvest, when psyllid pressure is high in fields in which tubers are destined for commercial storage.

(1) Background: The wheat curl mite (Aceria tosichella Keifer) is a key pest of wheat (Triticum aestivum L.) worldwide. While a number of wheat cultivars resistant to the mites have been employed to minimize the impact on the yield and quality of grain, little is known regarding the mechanisms underlying host plant resistance. Therefore, the goal of this study was to explore changes in transcriptome of resistant and susceptible wheat in order to quantify the molecular changes that drive host plant resistance. (2) Methods: Two varieties, wheat curl mite-susceptible (Karl 92) and wheat curl mite-resistant (TAM112) wheat, both at 2-week postemergence, were used in this study. Half of the plants were exposed to wheat curl mite herbivory and half remained mite-free and served as controls. Transcriptome changes were quantified using RNA-seq and compared among treatments to identify genes and pathways affected by herbivores. (3) Results: We identified a number of genes and pathways involved in plant defenses against pathogens, herbivores, and abiotic stress that were differentially expressed in the resistant wheat exposed to wheat curl mite herbivory but were unaffected in the susceptible wheat. (4) Conclusions: Our outcomes indicated that resistant wheat counteracts wheat curl mite exposure through effective induction of genes and pathways that enhance its defense responses.