Curly top on sugar beets (Beta vulgaris) caused by Beet severe curly top virus or closely related species is a considerable problem in arid growing regions of the western United States. Two insecticide seed treatments, Poncho Beta (60 g a.i. clothianidin + 8 g a.i. beta-cyfluthrin/100,000 seed) and Gaucho (45 g a.i. imidacloprid/100,000 seed), and four sugar beet hybrids varying in curly top resistance were evaluated for their influence on the control of curly top in comparison with untreated checks. Plots were established at two locations in southern Idaho in 2005 and evaluated for curly top. Moderate to severe curly top due to natural inoculum and leafhopper infestations occurred at both locations. Untreated, the four hybrids performed as expected with the fewest curly top symptoms on PM21 and the most on Monohikari. Both insecticide treatments lowered curly top ratings compared with the untreated check, but Poncho Beta reduced symptoms more than Gaucho as the season progressed. Poncho Beta led to increased yield and estimated recoverable sugar across all hybrids at harvest, particularly on the more susceptible hybrids. When considering the yield parameters for only the most resistant hybrids individually, Poncho Beta did not always outperform Gaucho. Poncho Beta provided a level of control that would justify its application as a supplement to host resistance under Idaho conditions.

KEY WORDS:Iron efficient, Iron inefficient, Iron-stress response mechanism, reductant, reduction of Fe 3+ by roots, root exudates, solution pH. ABSTRACT Iron-efficient and Fe-inefficient tomato (Lycopersicon esculentum Mill; T3238FER and T3238fer, respectively) and soybean (Glycine max (L.) Merr.; A7 and T203, respectively) were grown in modified Hoagland solutions with varying levels of Fe (0, 0.025, 0.05, and 0.75 mg Fe L -1 ). The release of H + ions, reductants and reduction of Fe 3+ to Fe 2+ by the root, and concentration of nutrients in plant leaves and roots were measured to determine if these factors interact during the Festress response mechanism. The FER tomato responded to Fe stress by increasing H ion and reductant release concurrently with increased reduction of Fe 3+ by the roots; all three reached maximum levels at the same time (day 7). Iron-stressed A7 soybean responded first with increased H + ion release and reduction by the roots, while reductant release lagged about 1 day behind. In both cases, increased concentration of leaf Fe corresponded to the time of maximum Fe-stress response. The Fe-423 424 CAMP, JOLLEY, AND BROWN inefficient T3238fer tomato and T203 soybean did not show any of these responses. When soybean plants (A7) were under Fe stress and then received either 0 or 0.20 mg Fe L -1 , the Fe-stressed plants responded to added Fe by reduced levels of H + ion and reductant release and reduction of Fe by the roots.We propose that the three steps of the Fe stress response mechanism--release of H + ions, release of reductants, and reduction of Fe 3+ by the roots--work together to favor maximum reduction of Fe 3+ . The H + ions provide maximum solubility of Fe, reduction by the roots provides reduced Fe, and reductants in the roots provide the environment to maintain the reduced Fe 2+ in the root.

Rhizomania caused by Beet necrotic yellow vein virus (BNYVV) and storage losses are serious sugar beet production problems. To investigate the influence of BNYVV on storability, six sugar beet cultivars varying for resistance to BNYVV were grown in 2005 and 2006 in southern Idaho fields with and without BNYVV-infested soil. At harvest, samples from each cultivar were placed in an outdoor ventilated pile in Twin Falls, ID and were removed at 40-day intervals starting at the end of October. After 144 and 142 days in storage, sugar reduction across cultivars averaged 20 and 13% without and 68 and 21% with BNYVV for the 2005 and 2006 roots, respectively. In the December samplings, frozen root area was 1 and 2% without and 25 and 41% with BNYVV for the 2005 and 2006 roots, respectively. Root rot was always worse with stored roots from BYNVV-infested soil in December, January, and February samplings. Root weight loss was variable in 2005; however, in 2006, an increase in weight reduction always was associated with BNYVV-infested roots. In order to prevent losses in rhizomania-infested areas, cultivars should be selected for storability as well as rhizomania resistance.

Sugar beet (Beta vulgaris) varieties were evaluated for disease resistance to curly top to establish if disease ratings made in inoculated nurseries correlated with disease ratings and yield in sugar beet crops exposed to natural disease outbreaks. Cultivars were planted both in inoculated curly top nurseries in Kimberly, ID, and in commercial cultivar trials in irrigated fields near Ontario, OR and Nampa, ID. Plants were evaluated for curly top using a rating scale of 0 (no symptoms) to 9 (dead). Moderate disease pressure in the Ontario (mean rating = 3.8) and Nampa (mean rating = 4.1) fields resulted in significant differences for disease rating, root yield, sugar content, and estimated recoverable sugar among cultivars. Disease ratings from both commercial fields were positively correlated (r = 0.91 and 0.82, P < 0.0001) with ratings from the inoculated nurseries. In commercial fields, root yield was negatively related to disease rating (r2 = 0.47 and 0.39, P ≤ 0.0004). For each unit increase in disease rating (increasing susceptibility), root yield decreased 5.76 to 6.93 t/ha. Thus, curly top nurseries reliably predict curly top resistant cultivars for commercial cultivation.

Nitrogen (N) management is critical in sugarbeet production to optimize yield and quality. Although, past research has been critical to improving and understanding sugarbeet N nutrition, continued research is needed to evaluate evolving varieties and management practices.