Spotlight on research: Wollastonite, silicon, pumpkins & powdery mildew

Welcome to Spotlight on Research! Every year, researchers publish thousands of studies and in hundreds of journals – and most aren’t really accessible to the general public. In the interest of increasing the accessibility of some cool research, in each episode, I’m going to summarize a recent study that I find interesting and potentially relevant to horticultural crop production in our region.

Today’s episode focuses on a study published in the December 2019 issue of HortTechnology. It was conducted by a team of researchers from Rutgers University in NJ.

You can read on, or, if you’d rather listen or watch so you can see the data from the paper – check out this 8-minute video clip.

The study focuses on wollastonite, a naturally-occuring mineral, calcium silicate. Wollastonite is a good source of silicon, and it also neutralizes soil acidity, similar to limestone. Silicon is the focus of quite a bit of research because, even though it is not officially regarded as an essential plant nutrient, it has been widely shown to beneficial to certain plants. In particular, for plants that are silicon accumulators (like rice, wheat and cucurbits), silicon has been shown to increase resistance to certain pathogens and some stresses, and in some cases, can enhance plant growth. This study focused on pumpkin, which is highly susceptible to powdery mildew.

The objectives of the study were: 1) to determine the optimum soil amendment rates for wollastonite to suppress powdery mildew in pumpkin, 2) to determine how well wollastonite neutralizes soil acidity compare with limestone, and 3) to determine whether pumpkin growth was affected by soil amendments with this mineral. Pumpkin seedlings of the variety ‘Connecticut Field’ were grown in native soil, with a relatively low pH of 4.9, amended with varying rates of either limestone or wollastonite – at rates ranging from 0.8 to 50 tons per acre. The young pumpkin plants were also inoculated with powdery mildew.

So what happened? Lime and wollastonite treatments increased pH and increased soil calcium(Ca). The wollastonite also increased soil silicon levels. When they measured nutrient uptake in the leaves, higher levels of both calcium and silicon were observed plants grown in wollastonite-amended soils. Interestingly, however, there may have been some cation competition, because potassium(K) and magnesium (Mg) levels were lower in plants grown in soils that had been amended at the highest rates.

There was a slight decrease in powdery mildew disease development in soils amended with wollastonite, as well as a slight increase in plant growth (as measured by shoot dry weight). These might have been correlated, since PM infects do reduce plant growth rates. Interestingly, increasing amendment rates didn’t increase these benefits. 

Putting it all together: This research showed that wollastonite, when applied to the soil, increased pH at rates similar to lime, increased plant-available Si and Ca, but decreased K and Mg uptake in pumpkin. It also increased growth of pumpkin seedlings, and slowed down the progression of powdery mildew. Before rushing out to purchase wollastonite, however, several important questions remain. How does soil type affect response to wollastonite? What effects might this have over the life of the plant? Powdery mildew often infects later in the growth cycle of the crop, rather than at the seedling stage here in NH. Will different plant species, or different varieties, behave similarly? What is the cost of wollastonite amendment as compared with alternative effective strategies to manage powdery mildew (e.g. disease-resistant varieties or fungicides), or to increase pH (lime, wood ash)? As with all good research projects, this one raises many more questions.

Do you have questions about this topic, or suggestions for other topics to explore in Spotlight on Research? If so, please reach out and let me know. Thanks for reading, and stay tuned for the next edition.  

Source: Li, Y., A-J Both, C.A. Wyenandt, E.F. Durner, and J.R. Heckman. 2019. Applying wollastonite to soil to adjust pH and suppress powdery mildew on pumpkin. HortTechnology 29(6):811-820.