Mobile is better.
The role and function of the systemic molecule, Xemium
By: Glen Forster
Growers are aware of the potential damage diseases can inflict on their crops. Fungal pathogens are mobile; they move throughout the plant tissue to gradually colonize the entire crop. So, if pathogens can move within the plant, shouldn’t your fungicide? This is precisely the reason why growers look for fungicides with systemic activity. Systemic fungicides move into and towards new growth within the plant to prevent or halt fungal growth. A major group of systemic fungicides are the SDHI fungicides or succinate dehydrogenase inhibitors. These fungicides act by inhibiting a crucial enzyme in the mitochondria or the powerhouse of the fungus. This shuts down the fungal cell’s energy supply and prevents the production of essential building blocks needed for growth. Fungi are particularly sensitive to fungicides that target mitochondria because this is where the cell’s fuel for survival is produced. A particularly unique SDHI fungicide called Xemium® has been a valuable compound for several years now and it’s changing the way we think about mobility.
Xemium is a third generation carboxamide, also known as fluxapyroxad. First and second generation carboxamides had a limited disease and application spectrum (FRAC 2016), whereas Xemium has a much broader spectrum across a host of different pathogens. Unlike most other SDHI chemistries, Xemium targets multiple stages of the fungus providing preventative, post-infection and residual efficacy (Figure 1). For example, it can inhibit both spore germination and mycelial growth in developing fungi. It provides control from early infection to later growth and future infection, giving growers greater application flexibility and efficacy. Like other SDHI fungicides, Xemium targets fungal mitochondria. But unlike the others, it reaches these mitochondria using its unique mobility characteristics. More specifically, Xemium can rearrange its chemical structure to maneuver through different types of plant tissue and fungal barriers. There are two forms of the molecule, the hydrophilic or “water loving” form that can move through cell walls and the plant’s vascular system and the hydrophobic or “water repelling” form that can adhere to and move through waxy layers and membranes of the plant.
Figure 1. Xemium demonstrates activity at multiple stages of fungi.
Once Xemium is applied, a portion quickly penetrates the leaf and moves into the plant’s water transport system, or the xylem, for quick movement to the tips of the leaves. It’s able to travel to portions of the plant that were not reached during spraying and eventually spreads throughout the entire cross-section of the leaf. The portion of Xemium that wasn’t taken up immediately, binds firmly to the waxy layer of the leaf. And thanks to its water-repelling properties, some of the active will remain on the leaf surface in waxy depots. These Xemium depots or deposits continuously release the active due to moisture or stress-related events. In other words, the plant is protected as it grows (Figure 2).
Figure 2. The distributon of Xemium throughout the plant tissue.
Systemic seed treatments make a difference.
Achieving a healthy, consistently emerged stand is key to a successful crop. Using a systemic seed treatment, particularly for pulses, protects the entire seedling during the critical growth stages and ensures that your crop gets that strong start. Seed treatments with Xemium move throughout the entire seedling providing superior disease control to young crops. Many seed treatments will move into the roots but not the shoots, so there is little efficacy on the aboveground portion of young plants. Xemium moves downward into the roots but it also moves toward new growth for improved germination and emergence (Figure 3). Overall, you’ll get protection from key seed- and soil-borne diseases in pulses like ascochyta, anthracnose, fusarium, rhizoctonia and pythium.
Figure 3. Xemium (shown in blue) travels from the seed throughout the seedling to provide consistent and continuous protection.
Source: BASF internal study, Germany, 2012.
Extended foliar disease protection.
Foliar diseases can significantly lower both the yield and quality of your pulses, so protecting the health of pulse crops is essential. The unique mobility properties of Xemium can help control foliar diseases like mycosphaerella in field peas, anthracnose in lentils and ascochyta blight in lentils and chickpeas. Because of the continuous redistribution and slow release of the active, the plant is protected for longer periods of time (Figure 4). But remember, just because Xemium provides extended protection to new growth, it won’t control disease that develops on older plant tissue. So as always, coverage is key.
Figure 4. Continuous release of Xemium over several days.
Xemium is a key active ingredient for several crops around the world, including wheat. In 2013, Smith et al. reported that Xemium showed stronger efficacy against key foliar diseases in wheat (septoria, tan spot and stripe rust) compared to other actives. They also found that plants treated with Xemium demonstrated greater water use efficiency, meaning the amount of water needed to produce the same amount of grain per hectare was significantly reduced compared to other fungicides. In Canada, a new research product called Nexicor™ is in the process of being registered. Nexicor combines three active ingredients, one of which is Xemium, to deliver superior leaf disease control in cereals. Research trials have demonstrated that Nexicor provides more consistent and continuous disease control for increased growth efficiency and greater yield potential.
- FRAC 2016. SDHI fungicides. http://www.frac.info/working-group/sdhi-fungicides
- Smith J, Grimmer M, Waterhouse S, Paveley N. 2013. Quantifying the non-fungicidal effects of foliar applications of fluxapyroxad (Xemium) on stomatal conductance, water use efficiency and yield in winter wheat. Communication Agriculture Applied Biological Science. 2013;78(3):523-35.
NEXICOR is a trade-mark, and XEMIUM is a registered trade-mark of BASF SE; all used with permission of BASF Canada Inc. NEXICOR fungicide should be used as part of a preventative disease control program. © 2017 BASF Canada Inc.